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5-2020

Application of biochar as an additive to enhance biomethane Application of biochar as an additive to enhance biomethane

potential in anaerobic digestion potential in anaerobic digestion

Cecilia B. Frias Flores [email protected]

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Application of biochar as an additive to enhance biomethane

potential in anaerobic digestion

By

Cecilia B. Frias Flores

A THESIS

Submitted in partial fulfillment of the requirements for the degree of

Master of Science in Sustainable Systems

Department of Sustainability

The Golisano Institute for Sustainability

Rochester Institute of Technology

May 2020

Author: _______________________________________________________________________

Sustainable Systems Program

Certified by: ___________________________________________________________________

Dr. Thomas A. Trabold

Associate Professor of Sustainability

Approved by: __________________________________________________________________

Dr. Thomas A. Trabold

Sustainability Department Head

Certified by: ___________________________________________________________________

Dr. Nabil Z. Nasr

Associate Provost and Director, Golisano Institute for Sustainability

2

NOTICE OF COPYRIGHT

© 2020


ii

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Application of biochar as an additive to enhance biomethane

potential in anaerobic digestion By


Submitted by Cecilia B. Frias Flores to fulfill a requirement for the degree of Master of Science in

Sustainable Systems and accepted on behalf of the Rochester Institute of Technology by the thesis

committee.

We, the undersigned members of the faculty of the Rochester Institute of Technology, certify that

we have advised and/or supervised the candidate on the work described in this thesis. We further

certify that we have reviewed the thesis manuscript and approve it in partial fulfillment of the

requirements of the degree of Master of Science in Sustainable Systems.

Approved by:

Dr. Thomas A. Trabold: __________________________________________________________

(Committee Chair and Thesis Advisor) Date

Dr. Jeffrey S. Lodge: _____________________________________________________________

Date

Dr. Eugene Park: ________________________________________________________________

Date

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SUSTAINABLE SYSTEMS PROGRAM

ROCHESTER INSTITUTE OF TECHNOLOGY

MAY 2020

Abstract

Golisano Institute for Sustainability

Rochester Institute of Technology

Degree: Master of Science Program: Sustainable Systems

Name of Candidate: Cecilia B. Frias Flores

Title: Application of biochar as an additive to enhance biomethane potential

in anaerobic digestion.

Energy and useful materials can be produced by applying biological and thermal conversion

processes such as anaerobic digestion and pyrolysis. Agricultural and industrial wastes seem to be

the most attractive substrates since they are essentially unlimited resources. Pyrolysis has been

used mostly for the conversion of biomass to bio-crude and biochar, a stable form of nearly pure

carbon that has application in many agricultural and environmental applications. There is a

widespread literature describing use of biochar as an additive to stabilize the anaerobic digestion

process. We studied the effects that biochar has on the biomethane potential (BMP) during

anaerobic digestion of a model food waste under mesophilic conditions (37ºC). Mixed food waste

(FW) and dry manure (DM) were first converted into biochar at 500 and 800ºC using a laboratory

pyrolysis furnace. Biochar loadings of 0, 0.5, 1, and 2 %g/gVS were added into 500 mL digester

vessels. It was found that biochar provides enhanced stability when added to AD because biochar

acts as a buffer in the system. Food waste biochar produced at 500ºC with a loading of 1% resulted

in an increase of 11.7% in BMP when compared to the control. It was determined that biochar

produced at lower temperature has lower pH and a greater effect in the upgrading of biomethane.

Based on the experimental results, a techno-economic analysis (TEA) model was developed to

understand the value that adding biochar would have to an operating digester, assuming a 10%

enhancement in methane production with 1% biochar addition, based on the total mass of waste

processed. The model included a sensitivity analysis in which an increase in food waste loading

of 1, 5, 10 and 20% to the AD system was studied. The TEA revealed that food waste tipping fees

drive the economics of working AD systems and that the addition of biochar has the possibility of

boosting the economics for scenarios where biochar is purchased at low to mid-range prices, or

when a pyrolysis system is installed on-site to produce biochar.

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ACKNOWLEDGEMENT

I would foremost like to express my deepest and most sincere gratitude to my thesis advisor

Dr. Thomas A. Trabold for his continuous support through this experience, his patience,

enthusiasm, and for believing in my potential. Thanks to his guidance and support, I was able to

complete my degree and take with me many life lessons. I could not have imagined having such a

great advisor and mentor who was able to help me grow as a researcher, student, and professional.

To the rest of my committee members, Dr. Jeffrey Lodge and Dr. Eugene Park, I thank you

for taking the time to review my work and offer your expert opinion, knowledge, and asking all

the right questions. I truly appreciate your contribution to my research.

I want to thank Michael T. Hughes for sticking by my side and being patient with me during

my many moments of stress. I appreciate everything you have done, and I am truly grateful to have

you by my side cheering me on. You have taught me so much.

Lastly, I want to dedicate this thesis to my mom Beatriz Flores Candelario and my sister,

Cindy B. Frias Flores for all the support they gave me from far away. We have always done

everything together and I could not have imagined a better family to have than you guys. I also

dedicate this thesis to my dad, Fulgencio Frias Polanco, who is no longer with us. I know that he

would be feeling so proud of me today for being able to finalize this chapter of my life. Thank you

mom and dad for making me into the person I am today. Thank you for all the scolding, the values,

the drive and the hard work you put into raising Cindy and me. I am truly grateful and proud to

have you as my parents.

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Since my family does not speak English, I re-wrote the message for them in Spanish.

Finalmente, le quiero dar las gracias y dedicarle esta tesis a mi mama, Beatriz Flores

Candelario, a mi papa, Fulgencio Frias Polanco, y a mi hermana, Cindy B. Frias Flores. Gracias a

ustedes tres soy quien soy hoy. Gracias por los consejos, el amor, la comprensión, y la sabiduría

que compartieron conmigo. Sin ustedes yo no podría estar aquí hoy. Gracias, mami y papi por

criarme con tanto amor e inculcar en mi las ganas de crecer, de aprender, y de dedicarme a las

ciencias. Gracias a sus esfuerzo y sacrificios hoy entiendo el valor que tiene vivir de manera

saludable, feliz, y llena de amor. Los amo mucho no sé qué hubiera sido de mi sin ustedes tres.

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TABLE OF CONTENTS

Page

List of Figures vii

List of Tables ix

Nomenclature x

Chapter 1. Introduction 11

Chapter 2. Biochar Production and Characterization 30

2.1. Introduction 30

2.2. Methods 30

2.2.1. Substrates and sample preparation 30

2.2.2. Biochar production 31

2.2.3. Surface area and pore size measurements 33

2.3. Results and Discussion 34

2.3.1. Biochar yield 34

2.3.2. Biochar alkalinity 35

2.3.3. Surface area and pore size analysis 36

Chapter 3. Effects of Biochar on Biomethane Production via Anaerobic Digestion 39


3.2. Methods 39

3.2.1. Inoculum and substrate preparation 39

3.2.2. Total and volatile solids determination 40

3.2.3. Automatic Methane Potential Test System II (AMPTS II) 41

3.2.4 Stress simulation run 44


3.3.1. Food waste biochar 44

3.3.2. Dry manure biochar 46

3.3.3. Digestate biochar 48

3.3.4. Stressed conditions with digestate biochar 50

Chapter 4. Techno-Economic Analysis of Biochar Addition in Anaerobic Digestion 54


4.2. Methods 55

4.2.1 Capital and operation and maintenance (O&M) costs 55

4.2.2 Revenue from enhanced electrical and thermal energy generation 58

4.2.3 Revenue from tipping fees 59

4.2.4 Revenue from renewable energy credits (RECs) 59

4.2.5 Revenue from carbon credit 60

4.2.6 Net Present Value (NPV) model 61


Chapter 5. Conclusions and Future Work 67

References 70

Appendix A. Raw biomethane (BMP) data and example calculation 79

Appendix A.1 Food waste biochar raw data 79

Appendix A.2 Dry manure biochar raw data 82

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Appendix A.3 Magnetic biochar raw data 87

Appendix A.4 Lag Phase 88

Appendix A.5 Example calculation of BMP 90

Appendix B. Net Present Value example calculation 91

LIST OF FIGURES

Page(s)

Figure 2.1 – Microwave furnace for biochar production under oxygen-free

(pyrolysis) conditions.

32

Figure 2.2 – Quantachrome NOVAe system for surface area and pore size

measurement.

33

Figure 2.3 – Results from the BET analysis. 38

Figure 3.1 – AMPTS II system for biomethane potential (BMP) measurement. 41

Figure 3.2 – Example of raw methane volume data generated by AMPTSII system

during mesophilic digestion of food waste.

43

Figure 3.3 - (a) Biomethane potential and (b) percent difference results (relative to

pure dog food) obtained from the run performed using food waste biochars

(FWBC500 and FWBC800).

45


pure dog food) obtained from the run performed using dry manure biochars

(DMBC500 and DMBC800).

47


pure dog food) obtained from the run performed using magnetic digestate biochar

(MGBC500 and MGBC800).

49

Figure 3.6 – Percent difference in ascending order for each run and biochar

loading.

50

Figure 3.7 – Biomethane potential results obtained from the run with the best

performing biochar.

52

Figure 4.1 – No-Incentive Case: Net Present Value for the addition of pyrolysis

biochar to a working AD system, including purchased pyrolysis system for biochar

production and low/mid/high costs of purchased biochar.

64

Figure 4.2 – Incentive Case: Net Present Value (NPV) for the addition of pyrolysis

biochar to a working AD system, including purchased pyrolysis system for biochar

production and low/mid/high costs of purchased biochar.

65

Figure 4.3 – Internal rate of return (IRR) determination for the case of on-site

biochar production with 5% additional food waste.

66

Figure A.1 – FWBC biogas production raw data 79

Figure A.2 – Average FWBC biogas production raw data 80

Figure A.3 – Average FWBC biogas production from day 11-30 80

Figure A.4 – DMBC biogas production raw data 82

Figure A.5 – Average DMBC biogas production raw data 83

Figure A.6 – Average DMBC biogas production from day 11-30 83

Figure A.7 – MGBC biogas production raw data 85

viii

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Figure A.8 – Average MGBC biogas production raw data 86

Figure A.9 – Average MGBC biogas production from day 11-30 86

Figure A.10 – Lag phase for biogas from runs (a) FWBC, (b) DMBC, (c) MGBC 88, 89

LIST OF TABLES

Page(s)

Table 1.1 – Review of literature on biochar addition to anaerobic digestion

processes

21-29

Table 2.1 – Yield and characterization data of biochar samples derived from

various feedstocks processed at 500 and 800ºC.

37

Table 3.1- Purina Beneful ® nutritional content as indicated on the product

package

40

Table 4.1 – NPV model inputs related to biochar equipment and materials,

assuming baseline food waste input in modeled AD plant

56

Table 4.2 – NPV model inputs related to anaerobic digester equipment and materials,

assuming baseline food waste input in modeled AD plant

57

Table 4.3 – NPV model inputs related to financial parameters 57

Table 4.4 – Conversion factors used in NPV calculations 57

Table A.1 – Raw data from FWBC run 81

Table A.2 – Raw data from the DMBC run 84

Table A.3 – Raw data from the MGBC run 87

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NOMENCLATURE

AD anaerobic digestion

BC biochar

BG biogas

BMP biomethane potential

Btu British thermal unit

CO2 carbon dioxide

CV calorific value

DMBC 500 dry manure biochar made at 500ºC

DMBC800 dry manure biochar made at 800ºC

EG energy generation

FWBC500 food waste biochar made at 500ºC

FWBC800 food waste biochar made at 800ºC

Gal gallons

gVS grams of volatile solids

HG heat generation

kg kilogram

kWh kilowatt-hour

L liters

lb pounds

MGBC500 magnetic digestate biochar made at 500ºC

MGBC800 magnetic digestate biochar made at 800ºC

MJ megajoules

MT metric ton

nel electrical conversion efficiency

nth thermal conversion efficiency

NPV net present value

NYSERDA New York State Energy Research and Development Authority

Py pyrolysis

RIT Rochester Institute of Technology

t time

yr year

x

11

CHAPTER 1

INTRODUCTION

The accumulation of waste from different product streams is known to negatively affect the

environment. Food waste has been identified as a major sustainability challenge (Trabold &

Babbitt, 2018), but excess food materials also have the potential for energy production by thermal

or biological conversion techniques (Ahmed & Gupta, 2010). However, since food waste is diverse

in composition, it represents a challenge in the coupling of multiple energy production systems

(Elkhalifa et al., 2019). Currently, many agricultural feedstocks and cow manure are used

commercially to produce value-added materials by means of chemical, biological and

thermochemical conversion processes.

Anaerobic digestion (AD) is a widely adopted process that converts biomass into biomethane

(CH4) by biological processes in the absence of oxygen. This process is very important because it

can help industries process their waste and lower energy costs since the biogas produced in the

process can be used to generate electricity and thermal energy. There are many variations of this

process, with the operation temperatures ranging from 35 ºC (mesophilic) to 70 ºC (thermophilic).

AD is a relatively low carbon footprint method to manage waste and increase its economic value

by turning waste into energy. Achieving high quality biogas (i.e., high CH4 content) starts by

selecting substrates that do not coat the available cellulose and impede microbial access for

degradation. Richer natural gas from AD is achieved by an increased biomethane content in the

biogas. This will minimize reduction of specific energy resulting from carbon dioxide dilution

(Masebinu et al., 2019).

12

Hydrolysis is the initial and one of the most important steps in anaerobic digestion, because it

starts the breakdown process of the substrate before the methanogens can digest the feedstock

material. Removing carbon dioxide, hydrogen sulfide, ammonia, and excess moisture can increase

the amount of methane produced by the system (Appels et al., 2008). The AD process needs to

have a well-working and balanced group of bacteria (acidogens, acetogens and methanogens) to

facilitate proper production of biogas. There is a need to ensure that the production of methane

starts by achieving a balance between acid producers and methanogens. Pretreatments have been

considered as a way to ensure balance, however, there is a need to consider other pathways like

the addition of adsorbents (Cooney et al., 2016).

A number of recent studies have demonstrated the importance of direct interspecies electron

transfer (DIET) in anaerobic digestion, whereby electrons are transferred directly from one cell to

another, thus serving an essential role in stabilizing AD processes by maintaining high

methanogenic rate under stressed conditions (Dubé et al., 2015). Three fundamental pathways have

been identified for facilitating DIET between electron donating bacteria and methanogenic

archaea: conductive pili, hair-like structures protruding from the cell surfaces; membrane-bound

conductive proteins; and secondary materials in the reaction medium that form a bridge between

bacteria and archaea (Park et al., 2018). The third pathway has been explored through numerous

studies using granular activated carbon (GAC) that is generally highly conductive and also has a

specific high surface area that supports the active microbial community (Yang et al., 2017; Ye et

al., 2018). For example, Hansen et al. (1999), studied the effect of activated carbon and sulfide in

the degradation of swine manure. They ran batch experiments for 68 days at 55 ºC, and activated

13

carbon was added at 0.5, 1, 2.5, and 5% w/w. At 2.5% the highest methane yield was produced.

The addition of activated charcoal doubled the amount of biomethane produced in comparison to

the control.

A potentially more sustainable alternative to GAC is biochar, a carbon-rich co-product of

thermochemical conversion of organic matter under reduced oxygen conditions. Pyrolysis is a

process that produces syngas, bio-oil and solid biochar by the recombination of the chemicals in

the biomass at temperatures between 300 and 800ºC in the absence of oxygen. The biochar from

pyrolysis is very stable and has many uses in agricultural, environmental and industrial

applications. For example, Gupta et al. (2018) produced and characterized biochar from different

sources, including rice waste (RWBC), mixed saw dust waste (MWBC), and mixed food waste

(FWBC), and added these materials as admixture for cement mortar. It was found that the porosity

in biochar increased the air volume when added to the mortar. Biochar also reduced the capillary

water absorption in the mortar (Gupta et al., 2018).

Gasification is another process for thermochemical conversion of biomass and involves oxygen

concentration well below the stoichiometric level needed for full combustion or incineration. A

recent review focused on the use of gasification and pyrolysis to treat the effluent of the anaerobic

digestion of forestry material, agricultural waste, municipal waste and sludge, among others (Xie

et al., 2015). They compiled diverse sources of literature data and concluded that higher

temperatures in gasification lead to the increase in harmful chemicals released to the atmosphere

or retained in the biochar. This is problematic because it will add an extra step of detoxification of

the biochar, which leads to more energy consumption. However, these same authors mentioned

14

that biochar pyrolysis does not produce potentially harmful releases since it is typically performed

at temperatures not higher than 800ºC. Another recent review by Weber & Quicker (2018)

discussed how different feedstocks and their varying composition yield different characteristics in

the biochar produced. Also, processing parameters like temperature and holding time of reaction

play an important role in the determination of surface area and active sites. Higher levels of

carbonization (typically occurring at higher temperatures) will lower the number of active sites.

Biochar is known to have relatively high porosity, high surface area, and a stable nature often

referred to as “recalcitrance” that minimizes oxidation to CO2.

Using pyrolysis to make highly stable carbonaceous materials is a sustainable alternative to

landfilling the solid effluent from industrial or agricultural processes. Biochar has previously been

considered a waste from the conversion of biomass into fuels. However, in recent years, biochar

has been viewed as a value-added by-product from the conversion of biomass, since it has been

linked to many commercial and agricultural applications (Inyang et al., 2010; Shen et al., 2016).

While there are many pathways to the production of biochar, slow pyrolysis has mostly been

considered because it provides multiple operating parameters that can be modified for specific uses

(Luz et al., 2018). For example, biochar adsorbs contaminants from antibiotic residues, oily

substances, pesticides, and metal ions dispersed in water. Because biochar is a porous and

carbonaceous material, it has also proven effective in the immobilization of bacteria and provides

support to the anaerobic digestion (AD) process. The addition of biochar to digesters has been

shown to shorten digestion starting time, thereby increasing biomethane potential (BMP) while

reducing acid stress (Cimon et al., 2020; Mumme et al., 2014).

15

Prior research on the integration of pyrolysis and anaerobic digestion systems has mainly focused

on how pyrolysis of AD effluent (also referred to as “digestate”) aids in upgrading material

characteristics like pH, surface area, pore size, and hydrophobicity. For example, bagasse digestate

was processed using pyrolysis and it was found that by employing anaerobic digestion the

physiochemical properties of the biochar had become more favorable for its use as a contaminant

inhibitor (Inyang et al., 2010). It is not yet clear the extent to which pyrolysis derived biochar from

various feedstocks aids in the increase of methane production during anaerobic digestion by

lowering the presence of inhibitors (Mumme et al., 2014). This is due to the many different

substrates that are currently used for the anaerobic digestion process (Pecchi & Baratieri, 2019).

Studies also found that adding biochar as an adsorbent agent to anaerobic digestion provides the

acclimatization of bacteria and reduces the concentration of inhibitors. Biochar creates a protective

layer around the microbes during anaerobic digestion that promotes the production of methane.

Organic adsorbents like biochar create a strong bond with the inhibitors, are hydrophobic

(beneficial because there are water insoluble inhibitors), have surface precipitation, and are porous.

Functional groups in biochar also influence pH level that attracts specific types of contaminants

(Fagbohungbe et al., 2017). The addition of biochar to high solids digestate also proved to act as

a stabilizing agent by controlling the access to nutrients to the bacteria and removing ammonia and

volatile fatty acids (Indren et al., 2020).

Activated carbon and biochar are similar materials, the main difference being that biochar is often

less inexpensive to make than activated charcoal, especially if derived from waste feedstocks, but

offers many of the same properties. As reviewed by Masebinu et al. (2019), biochar adsorbs

inhibitors like acetate and ammonia, and promotes the creation of a microbial biofilm that increases

16

colonization of methanogens. From the extensive literature summarized in Table 1.1 and reviews

published in the past several years (Fagbohungbe et al., 2017; Luz et al., 2018; Masebinu et al.,

2019; Pan et al., 2019; Pecchi & Baratieri, 2019; Qiu et al., 2019; Zhang et al., 2018; Zhang et al.,

2020b), it is now known that biochar addition can enhance anaerobic digestion in a number of

ways:

• Accelerating the hydrolysis reaction, and thus shortening the lag time before biomethane

production begins.

• Increasing the maximum biomethane yield normalized by the total mass of volatile solids

(units of mL/g VS).

• Increasing the reaction rate constant, i.e., achieving the maximum biomethane yield in a

shorter time.

• Providing stability when the digester is under “stressed” conditions, such as unusually high

or low pH.

• Upgrading biomethane to “pipeline” quality by adsorbing CO2, hydrogen sulfide (H2S) and

other contaminants.

Shen et al. (2015) performed anaerobic digestion of sludge and added corn stover biochar at 1.82

to 3.64 %g/g TS substrate to determine the role that biochar plays in upgrading the anaerobic

digestion process. They found that biochar facilitates the hydrolysis of substrates during anaerobic

digestion and lowers the amount of CO2 in the system. Without adding any biochar, the highest

biogas production was achieved; however, addition of 1.82 %g/g TS substrate of biochar produced

the highest amount of biomethane which represented an increase of about 42% biomethane from

the control. Similarly, in another study, waste activated sludge was pyrolyzed at 300, 500 and 700

17

ºC and added to digesters. It was found that sludge derived biochar did not provide a significant

increase in methane potential, however, more pores are available at higher temperatures and

temperature affected the ability of biochar to enhance the AD process (Wu et al., 2019b). Another

study by Sunyoto et al. (2016) investigated the effect that biochar addition had in two-phase

anaerobic digestion of bread and heated sludge. They loaded 8.3, 16.6, 25.1 and 33.1 g/L of biochar

into small-scale bottle reactors. It was found that there was a significant difference in the amount

of methane and hydrogen produced between digestion with biochar and the control. Among the

three biochar loadings, there was not much difference, but the highest amount of methane was

found at a loading of 8.3g/L.

In mesophilic digesters (i.e., running at a nominal temperature of 37 ºC) with a dosage of biochar

added, it was found that methanomicrobia accounted for 44% of archaea (Lü et al., 2019). Which

means that adding the biochar promoted an enrichment of the bacterial community. Ma et al.

(2019) also supported these results, they studied how adding biochar to mesophilic air-dried

chicken manure helped in stabilizing AD and the consumption of raw material in the process. They

determined that biochar addition to the AD increased the specific biomethane potential by 12%

and suppressed the production of inhibitors. Addition of biochar resulted in the production of more

methanogens and enhanced methane production because biochar acts as a buffer in AD, while

increasing propionic acid degradation. The addition of biochar can also decrease the retention time

of the sludge by accelerating methane production, even when not representing a significant

increase in BMP (Cimon et al., 2020). Pan et al. (2019) made biochar from chicken manure,

discarded fruitwood, and wheat straw to study their effects on the AD of chicken manure. They

studied the characteristics of each biochar and differences in conversion with varying pyrolysis

18

temperatures, ranging from 350 to 550ºC. They found pH and specific surface areas were higher

as temperatures increased and biochar proved helpful in the degradation of the solid material

because it improved the hydrolysis process.

Studies have up to this point discussed that there has been an increase in BMP of 10-15% or less

with an improved stability in the AD process by the addition of biochar (Mainardis et al., 2019;

Pan et al., 2019; Rasapoor et al., 2020; Wang et al., 2020). The pH levels found in biochar have

shown to be one of the main characteristics which determine the activity of the surface in biochar

and its relationship with the microorganisms in AD (Yin et al., 2020), and thus it is expected that

pH is an important parameter to consider in understanding the potential of biochar to enhance

biomethane potential and AD system stability.

The study of the effects that magnetic biochar has on the enhancement and stability of digesters

has become a new way to couple pyrolysis and anaerobic digestion (Alberto et al., 2019). Magnetic

biochar has proven to allow higher interactions because it was found that oxygen containing

molecules like acids in the system will likely be adsorbed with more ease to the active sites (Du et

al., 2020). Magnetic biochar seems to facilitate interaction with the bacteria cell walls that

increases adhesion and promotes access to the substrate during AD. Shao et al. (2019) studied

how biochar stabilizes AD under stressed conditions. Conductive materials can be helpful during

AD because they can enhance the production of methanogens, meaning that adding magnetic

materials can act as a catalyst in the system and allow for digestion to continue when the conditions

become unstable.

19

Despite the extensive literature summarized in Table 1.1, there are only a few papers that studied

the waste management system of particular interest to our research group, i.e., mesophilic

anaerobic digestion of food waste. In the Upstate New York region, mesophilic co-digestion of

food waste with dairy manure has become a fairly common method of converting waste from food

processors and retailers such as groceries stores, and the expectation is that AD plants will continue

to expand as we approach January 2021, when the State’s commercial food waste ban goes into

effect. We are therefore specifically interested in the potential benefits of biochar in anaerobic

digestion of food waste in the temperature range of about 35 – 40 ºC, which applied to only 10 of

the papers in Table 1.1. Based on the comprehensive assessment of the literature, the current

research project was structured to address the following compelling research questions:

• What are the properties of biochar derived from selected waste feedstocks available in the

local food supply chain, and pyrolyzed at different temperatures?

• What impacts do these biochar materials have on the mesophilic anaerobic digestion of a

model food waste substrate, in terms of maximum biomethane potential?

• Does biochar addition benefit the AD process under “stressed” reactor conditions with

unusually low pH?

• Can biochar addition to anaerobic digesters be economically viable at commercial scale,

based on the balance between measured benefits in reactor performance and estimated

increases in capital and operating costs?

These research questions have been addressed in the following chapters. Chapter 2 provides a

description of the biochar production methods and results of characterization measurements.

Chapter 3 describes the main part of the research covering extensive biomethane potential

20

experiments involving dog food as a model mixed food waste substrate, coupled with a wide range

of biochar materials identified in Chapter 2. Chapter 4 covers a techno-economic analysis (TEA)

based on computation of net present value (NPV) and identifies conditions under which the NPV

is positive and thus biochar addition may be viable for investment. Finally, the main conclusions

and outcomes of the research, and recommendations for future work, are presented in Chapter 5.

21

Table 1.1 – Review of literature on biochar addition to anaerobic digestion processes

Biochar Anaerobic digestion Reported impact on AD process Reference

Feedstock Tbp Amount Substrate TAD waste forest

industry wood

450-

550

0.2-3.7 g/g

VS

acidified municipal

sludge

55 Rate of methane production increased 192–461% from

control in the first 16 days. This increase was followed by

an early stationary methane production phase and a

reduction of total methane yield by up to 25%.

Cimon et al. (2020)

wood pellets wheat

straw

sheep manure

680-

770

1:1 ratio of

biochar to

poultry

litter dry

mass

poultry litter 37 The addition of wood pellet biochar provided a 32%

increase to the methane yield compared with control. The

addition of biochar produced from either wheat straw or

sheep manure had detrimental effects on digester

performance. The addition of wood pellet biochar pre-

loaded by placing it in a high-solids digester for 90 days

provided a 69% increase in the total methane yield, 44%

increase in the peak daily methane yield and a 33%

reduction in the lag time compared with controls.

Indren et al. (2020)

pine sawdust

manuka wood

chips

poultry waste

500-

550

10, 20, 30

g/L

organic fraction of

municipal solid

waste (OFMSW)

35 Using 20 g/L biochar significantly increased the rate of

AD for all types of biochar, as confirmed by

thermogravimetric results. The physical properties of the

additives, including electrical conductivity and surface

area, were found to influence only the rate of AD process

and not the biogas production yield.

Rasapoor et al. (2020)

rice husk

peanut shell

straw

sawdust

Also purchased

coconut shell and

shrub biochars.

600 0.5, 1, 2,

4%

straw

cow manure

38 Cumulative methane yield with coconut shell biochar was

higher than that without a biochar (319.44 vs. 282.77 mL/g

VS). AD with biochars had a secondary methane yield

peak, whereas control groups did not show this

phenomenon. A suitable dosage (e.g., straw biochar of

2%) improved cumulative methane yield, but excessive

addition (4%) could inhibit AD.

Shen et al. (2020)

sawdust (SDBC) 300

500

700

15 g/L sewage sludge

mixed cafeteria food

waste

35 SDBC prepared at 500°C performed better in enhancing

CH4 production than other SDBCs. Analyzing the crucial

electro-chemical characteristics of the SDBCs revealed

that the excellent electron transfer capacity of SDBC was

significant to stimulate methanogenesis promotion. Long-

Wang et al. (2020)

22

term semi-continuous operation further confirmed that

adding SDBC to AD system increased the maximum

organic loading rate (OLR) from 6.8 to 16.2 g VS/L/d.

corn stover 600 1.82, 2.55,

3.06 g/gTS

primary sludge (PS)

waste activated

sludge (WAS)

55 Dosing biochar in digester improved methane content from

67.5% to 81.3–87.3% and enhanced methane production

by 8.6–17.8%. In a continuous test over 116 days, the

volatile solids (VS) destruction in the biochar-dosed

digester increased by 14.9%, resulting in a 14% reduction

in the volume of digestate for disposal.

Wei et al. (2020)

waste wood pellets 700-

800

7.5, 15,

22.5, 30,

37.5 g/L


waste

55 Optimal dosage range of biochar was determined as 7.5 to

15 g per L working volume based on lab-scale batch AD.

Effects of biochar with different particle sizes at a model

dosage of 15 g/L were evaluated in a semi-continuous AD

experiment. Results showed that all the examined biochars

with different particle sizes (< 50 μm to 3 cm)

substantially enhanced the average methane yields (0.465–

0.543 L/gVS) compared to control digesters which failed

due to overloading (≥ 3.04 gVS/L/d). No significant

difference in methane yields, however, was observed

among digesters with different particle sizes of biochars,

except for 1–3 cm.

Zhang et al. (2020b)

algal biomass 500-

600

15 g/L mixed cafeteria food

waste

algal biomass

35

55

Under batch co-digestion, the highest co-digestion synergy

was observed for a mixture of 25% food waste and 75%

algal biomass. During semi-continuous co-digestion of

25% food waste-75% algal biomass mixture, biochar

amended digesters exhibited a 12–54% increase in average

methane yield (275.8–394.6 mL/gVS) compared to the

controls.

Zhang et al. (2020a)

brewer’s spent

grain

300 1, 3, 8, 10,

20, 30,

50%

brewer’s spent grain 37 The highest biogas production rate resulted from 5%

biochar addition, significantly higher than all other biochar

loadings. The 5% biochar dose also resulted in the

maximum production of biogas from the substrate and the

highest reaction rate constant, but neither was significantly

different from the 0% biochar case.

Dudek et al. (2019)

23

commercial

biochar (CB) and

local biochar

derived from

municipal sludge

500 0.25 g/day

added to

1.5L CSTR


waste

35-37 Both local biochar (LBC) and commercial biochar (CBC)

showed similar efficiency that enhanced high methane

yield (5%) compared to the control, while stimulating

reactor process stability at high organic loading rate

(OLR).

Giwa et al. (2019)

pine 800 10 g/L oil 35,

55

Powdered biochar was able to adjust the microbial

communities and further increased CH4 production by

13.3% in thermophilic digesters. Granular biochar

enhanced the maximum CH4 potential by 32.5% under

mesophilic condition, which was most promising from the

perspective of energy recovery.

Lü et al. (2019)

fruitwoods 550 5% chicken manure 35 The average specific methane productions of 0.18

L/gVSadded and 0.17 L/gVSadded were achieved without

biochar at the organic loading rate (OLR) of 3.125 and

6.25 g VS/L/d, respectively. An increase of 12% in

methane production was obtained in the presence of

biochar at the two operational OLRs.

Ma et al. (2019)

red spruce 650 0.2 g/gVS brewery spent grain

(BSG), spent yeast

(BSY), etc.

35 Biochemical methane potential tests revealed high

methane potential of spent yeast, up to 486.9 NL CH4/kg

VSadded, and spent grain, up to 356.2 NL CH4/kg VS

added. Granular activated carbon and biochar were added

to selected tests to evaluate an eventual increase in

methane yield; a noticeable effect was observed in

particular on spent yeast, due to the enhanced

microorganism activity and C/N ratio optimization.

Mainardis et al. (2019)

wheat straw

fruitwood

chicken manure

350

450

550

5% based

on TS

chicken manure 35 Substantial improvements in methane production were

observed for all nine types of biochar. Fruitwood char

pyrolysed at 550°C increased the methane yield by 69%

from the control. Characteristic analysis indicated that

fruitwood char pyrolysed at 550 °C exhibited the largest

specific surface area and highest total ammonia nitrogen

reduction capacity.

Pan et al. (2019)

hardwood NR 5-30 g/L wheat straw 55 10 g/L of hardwood biochar led to 2-fold increment in

methane yield (223 L/kg VS) compared to the control (110

L/kg VS). However, increasing the concentration of

Paritosh and

Vivekanand (2019)

24

hardwood biochar did not help in significant increase in

methane yield and raised pH and alkalinity up to 8.3 and

24.3 g/L respectively.

wood 800-

900

2 g/L acetate 35 External voltage and additives (biochar and zeolite) were

applied simultaneously and independently to laboratory-

scale anaerobic reactors for further clues of DIET-

enhancing mechanism. Biochar was discovered to benefit

only stressed scenarios caused by external voltage or

microbial inactivity, but express no significant influence

on well-operating ones.

Shao et al. (2019)

waste activated

sludge

300

500

700

10 g/L waste activated

sludge

37 Hydrochar better promoted methane production compared

with pyrochar. The highest cumulative methane yield of

132.04 ± 4.41 mL/g VSadded was obtained with addition of

hydrochar produced at 180oC. In contrast, the

pyropchar produced at 500 and 700oC showed a slightly

negative effect on methane production.

Wu et al. (2019a)

dairy manure 350 1 and 10

g/L

dairy manure 20,

35,

55

Compared with AD without any biochar, the cumulative

methane and yield in the AD with 10 g/L biochar were

increased to 27.65% and 26.47% in psychrophilic, 32.21%

and 24.90% in mesophilic and 35.71% and 24.69% in

thermophilic digestions. The addition of manure biochar

shortened the lag phases of AD at all temperatures in the

study.

Jang et al. (2018)

sawdust 500 10 g/L mixed cafeteria food

waste

waste activated

sludge

55 Batch experiments were conducted using biochar (BC) to

promote stable and efficient methane production from

thermophilic co-digestion of food waste (FW) and waste

activated sludge (WAS) at feedstock/seed sludge (F/S)

ratios of 0.25, 0.75, 1.5, 2.25, and 3. The results showed

that the presence of BC dramatically shortened the lag

time of methane production and increased the methane

production rate with increased organic loading.

Li et al. (2018)

ampelodesmos

mauritanicus

biomass

450

500

550

5g in 1.5L

water

activated food waste 37 The modified Gompertz equation was used to describe the

influence of biochar production temperature on methane

conversion. A lag phase of 1.8, 2.2 and 3.8 days

respectively for B450, B500 and B550, has been

Luz et al. (2018b)

25

estimated, showing an inverse proportionality to the

biochar production temperature. The biomass to biogas

energy conversion analysis reveals a reduction in the

efficiency with increased biochar production temperature.

canola meal

switchgrass

Ashe juniper

400-

900

1% glucose

aqueous phase of

algal liquefaction

37 Biochars synthesized at intermediate temperatures (400

and 500oC) significantly increased methane yield and

reduced the lag time required for methane formation.

Shanmugam et al.

(2018)

rice straw 500 4 g/L synthetic wastewater 35 Two upflow anaerobic sludge blanket (UASB) reactors

were built in this study. With the addition of biochar, the

lag time of methanogenesis was shortened by 28.6%, and

the strengthening factor of COD removal rate reached 1.6.

Wang et al. (2018b)

sawdust 500 2, 6, 10, 15

g/L

dewatered activated

sludge

synthetic food waste

35 Compared with conventional operation, biochar addition

effectively shortened the lag time by 27.5–64.4% and

increased the maximum methane production rate by

22.4%–40.3%. With a biochar dosage of 15 g/L, the

system performed well under an organic loading rate as

high as 3 g substrate/g inoculums.

Wang et al. (2018a)

Corn cob

Sawdust

Waste cardboard

Walnut shell

NR 0.18 wt% dairy manure

37 Adding carbon into AD systems significantly improved the

biogas yield and COD removal rate by 30-70% and 74-

129%, respectively, compared to the reference

system. Carbon additives with higher BET specific surface

area are responsible for improving the AD efficiency by

providing sites where substrate accumulate and thereby

promote high localized substrate concentrations.

Yun et al. (2018)

fruitwoods 550 5% chicken manure

15-65 Comparison of the added biochar reactor with a control

reactor without biochar operated at 35°C showed that the

addition of biochar reduced the lag phase by 41%,

enhanced the maximum methane production rate by 18%,

and reduced the hydrogen sulfide by more than 95%,

although no difference was observed in the cumulative

methane production.

Liang et al. (2017)

walnut shell 900 0.96-3.83

g/gVS

food waste

WWTP sludge

37 &

55

Average methane volume concentration in biogas

increased up to 98.1%, with fine biochar outperforming

coarse biochar.

Linville et al. (2017)

26

magnetic biochar

from rice straw and

FeCl3

500 0.5% w/w organic fraction of

municipal solid

waste (OFMSW)

35 Methane production in AD treatment with magnetic

biochar fabricated under 3.2 g FeCl3:100 g rice-straw ratio

increased by 11.69% compared with control treatment

without biochar addition, due to selective enrichment of

microorganisms participating in anaerobic digestion on

magnetic biochar. AD treatment with magnetic biochar

resulted in 38.34% decrease of methane production

because of the competition of iron oxide for electrons.

Qin et al. (2017)

corn stover

(CSBC)

pine (PBC)

NR 0.25-1.0

g/day

WWTP sludge 55 Both CSBC and PBC promoted the substrate utilization,

methane productivity, and process stability of AD, while

CSBC showed superior potential. CSBC enhanced

methane content in biogas (CH4%) and methane

production rate by up to 25% and 37% respectively in

comparison to the control, with maximum CH4 of 95% and

CH4 yield of 0.34 L/g volatile solid (VS)-added being

achieved at steady state.

Shen et al. (2017)

wheat bran

hardwoods

orchard prunings

500-

800

25 g/L food waste

fermentate

20 Methanogenic conversion proceeded at a rate up to 5 times

higher than non-biochar control. Electron donating

capacity is the primary parameter that dictates biochar

performance.

Viggi et al. (2017)

vermicompost 500 5, 10, 15,

20%

kitchen waste

chicken manure

35 Chicken manure digestion was not initiated at higher

organic loading of 50 g TS/kg, while it worked well with

5.0% vermicompost biochar (VCBC) or unconverted

vermicompost (VC). Kitchen waste was not digested even

though VC or VCBC was increased to 15% and 20%.

Wang et al. (2018)

fruitwoods 800-

900

0.2-2.5 g/g

DW waste


waste

35 Biochar treatments at inoculum-to-substrate ratio (ISR) =

2, 1, and 0.8 shortened the lag phase of digestion by

−20.0%–10.9%, 43.3%–54.4%, and 36.3%–54.0%, and

raised the maximum methane production rate by 100%–

275%, 100%–133.3%, and 33.3%–100%, respectively,

compared to control without biochar.

Cai et al. (2016)

pinewood 650 Surface

area-to-

volume

molasses wastewater 34 Two different carrier materials, i.e., carbon felt and

biochar, with similar surface properties were evaluated for

their potential to stabilize anaerobic digestion of these

wastewaters via active enrichment of the methanogenic

De Vrieze et al. (2016)

27

ratio =

0.015 m2/L

community. Initial stable methane production values

between 620 and 640 mL CH4 L−1 day−1 were reported in

each treatment. At the end of the experiment, methane

production decreased more than 50 %, while VFA

increased to values up to 20 g COD L−1, indicating severe

process failure, due to the high potassium concentration in

these wastewaters.

wood

coconut shell

rice husk

450 citrus peel-

to-biochar

ratios of

1:1, 1:2,

1:3 and 1:1

citrus peel waste 35 The presence of biochar had two effects: a reduction in the

length of the lag phase and greater production of methane

relative to citrus peel waste only incubations. The

microbial lag phases decreased with increase in citrus peel

to biochar ratios, with 2:1 having the longest lag phase of

9.4 days and 1:3, the shortest, with the value of 7.5 days.

The cumulative methane production in incubations

containing biochar and citrus peel ranged from 163.9 to

186.8 ml CH4 g VS-1, while citrus peel only produced

165.9 ml CH4 g VS-1.

Fagbohungbe et al.

(2016)

fruitwoods 800-

900

10 g/L glucose solutions

with different total

ammonia nitrogen

stress levels

35 Compared to the control treatment without biochar

addition, treatments that included biochar particles 2-5

mm, 0.5-1 mm and 75-150 μm in size reduced the

methanization lag phase by 23.9%, 23.8% and 5.9%,

respectively, and increased the maximum methane

production rate by 47.1%, 23.5% and 44.1%, respectively.

Lü et al. (2016)

holm oak 650 5 and 10% bio-waste 40 Biochar was tested with a setup that simulated an

industrial-scale biogas plant. Both biogas and methane

yield increased around 5% with a biochar addition of 5%,

based on organic dry matter biochar to bio-waste. An

addition of 10% increased yield by around 3%.

Meyer-Kohlstock et

al. (2016)

pinewood

white oak

NR 2.20-4.97

g/g

WWTP sludge 37 &

55

The biochar-amended digesters achieved average methane

content in biogas of up to 92.3% and 79.0%,

corresponding to CO2 sequestration by up to 66.2% and

32.4% during mesophilic and thermophilic AD,

respectively. Biochar addition enhanced process stability

by increasing the alkalinity, but inhibitory effects were

observed at high dosage.

Shen et al. (2016)

28

pine sawdust 650 8.3, 16.6,

25.1, 33.3

g/L

white bread

(simulating

carbohydrate-rich

food waste)

35 The results showed that biochar addition increased the

maximum production rates of hydrogen by 32.5%

and methane 41.6%, improved hydrogen yield by 31.0%

and methane 10.0%, and shortened the lag phases in the

two phases by 36.0% and 41.0%, respectively. Biochar

addition also enhanced VFA generation during hydrogen

production and VFA degradation in methane production.

Sunyoto et al. (2016)

bamboo NR NR Bamboo industry

wastewater

32 Two anaerobic membrane bioreactors were operated for

150 days to treat bamboo industry wastewater, and one of

them was enhanced with bamboo charcoal (biochar).

During the steady period, average chemical oxygen

demand (COD) removal efficiencies of 94.5 ± 2.9% and

89.1 ± 3.1% were achieved with and without biochar,

respectively. A higher biogas production and methane

yield were also observed in the reactor with biochar.

Xia et al. (2016)

fruitwood 800 10 g/L pulp sewage

glucose

35 The addition of 0.5-1 mm biostable biochar to mesophilic

anaerobic digesters inoculated with crushed granules (1 g-

VS/L) and fed with 4, 6 and 8 g/L glucose shortened the

methanogenic lag phase by 11.4%, 30.3% and 21.6% and

raised the maximum methane production rate by 86.6%,

21.4% and 5.2%, respectively, compared with the controls

without biochar. 75 μm biochar further shortened the lag

phase by 38.0% and increased the methane production rate

by 70.6% at 6 g/L glucose loading.

Luo et al. (2015)

Corn stover NR 1.82 – 3.64

g/gTS

WWTP sludge 55 The biochar amended digesters produced near pipeline-

quality biomethane (>90% CH4 and <5 ppb H2S),

facilitated CO2 removal by up to 86.3%, boosted average

CH4 content in biogas by up to 42.4% compared to the

control digester. The biochar addition enhanced the

methane yield, biomethanation rate constant and maximum

methane production rate by up to 7.0%, 8.1% and 27.6%,

respectively. The biochar addition also increased alkalinity

and mitigated ammonia inhibition, providing sustainable

process stability for thermophilic sludge AD.

Shen et al. (2015)

29

NR NR NR artificial ethanol-

rich wastewater

37 Graphite, biochar, and carbon cloth all immediately

enhanced methane production and COD removal. The

COD removal efficiency in the three reactors

supplemented with conductive materials was all higher

than 93%, whereas the COD removal in the control reactor

averaged only 83%.

Zhao et al. (2015)

Mixed paper

sludge and wheat

husks

500 cattle slurry

maize

maize silage

42 For pyrochar, no clear effect on biogas production was

observed, whereas hydrochar increased the methane yield

by 32%. This correlates with the hydrochar’s larger

fraction of anaerobically degradable carbon (10.4% of

total carbon, pyrochar: 0.6%).

Mumme et al. (2014)

corn stalk pellets 400 1:1 aqueous phase liquid

(APL) from

intermediate

pyrolysis of biomass

40 Biochar addition increased yield of methane (60 ± 15% of

theoretical) with respect to pure APL (34 ± 6% of

theoretical) and improved the reaction rate. On the basis of

batch results, a semi-continuous biomethanation test was

set up, by adding an increasingly amount of APL in a 30

ml reactor preloaded with biochar (0.8 g ml-1).

Torri & Fabbri (2014)

Japanese cedar NR NR Crude glycerol

WWTP sludge

35 Methane yield from a charcoal-containing reactor was

approximately 1.6 times higher than that from a reactor

without charcoal, and methane production was stable over

50 days when the loading rate was 2.17 g chemical oxygen

demand (COD) L-1 d-1.

Watanabe et al. (2013)

rice husks 900-

1000

1-3% of

substrate

dry mass

cattle manure 35 Incorporation of 1% (DM basis) of biochar in a batch

biodigester increased gas production by 31% after 30 days

of continuous fermentation. There were no benefits from

increasing the biochar to 3% of substrate DM. Methane

content of the gas increased with the duration of the

fermentation but was not affected by the presence of

biochar in the incubation medium.

Inthapanya et al.

(2012)

charcoal powder NR 5% cow slurry 35 Batch: biogas yield increased 17.4%

Continuous: biogas yield increased 34.7%

Kumar et al. (1987)

NR: not reported

TAD: temperature of anaerobic digestion (ºC)

Tbp: temperature of biochar production (ºC)

30

CHAPTER 2

BIOCHAR PRODUCTION AND CHARACTERIZATION

2.1 Introduction

This chapter highlights the production and characterization of biochar using pyrolysis at two

different temperatures. Pyrolysis is a proven way to reduce waste while producing a low cost and

eco-friendly substitute for activated carbon. Its high stability, ease of production and low capital

cost are some of the most desirable characteristics. Biochar has many applications that range from

various industrial uses to agriculture, pharmaceutical and building materials. There are many

feedstocks currently being used to make biochar, including a wide range of waste materials such

as food waste. The material from which biochar originates, coupled with the specific pyrolysis

process conditions, will largely determine the characteristics of the biochar and its potential uses.

This study is specific to the understanding of the characteristics of biochar from three different

waste streams which can aid in the enhancement of anaerobic digestion. The three feedstocks (food

waste, dry manure, and treated digestate) were obtained, dried, and homogenized prior to analysis

and conversion. The methods and results are highlighted below.

2.2 Methods

2.2.1 Substrates and sample preparation

Materials for the experiments were obtained from various sources, dried and stored until further

analysis. Dry manure was obtained from a local dairy farm located in Covington, NY. The samples

were stored in a refrigerator until further processing. Food waste from the Rochester Institute of

Technology’s food vendors was collected and dehydrated for 10 hours and stored until further

31

processing. Prior to producing biochar, the samples were further dried in an oven at 105oC for 24

hrs.

2.2.2 Biochar production

A high temperature furnace with a coupled microwave generator (Al-25/1700) was obtained from

Zicar Ceramics Inc. (1712GS FL, Figure 2.1). As described by Yakovlev et al. (2011) , the system

has a cubic metal frame with insulation material containing 80% alumina (Al2O3) and 20% silica

(SiO2). The system can reach temperatures up to 1700 ºC. The system is cleaned every three runs

using air as the medium gas to burn out impurities. The system allows for the usage of any inert

gas for the process and has a microwave system included, although this feature was not used in the

current research program. The furnace allows for the placement of up to five crucibles and the

exhaust system includes a stainless-steel tube placed above the furnace where the condensed bio-

oils can be collected and discarded or stored for future analysis.

The pyrolysis process was conducted by placing five crucibles containing the raw dry material

inside the furnace. The amount of biomass placed in each crucible varied within samples, however

they were all 2/3 of the crucible space. The system was heated at a rate of 10ºC/min until the

desired final temperature was reached, and there was a 1-hour hold time and then the system was

cooled to 60ºC prior to removal. Each substrate was processed in a nitrogen environment at two

different temperatures (500 and 800ºC). The biochar samples were labeled based on their

composition and processing temperature. Digestate biochar was identified as MGBC500 and

MGBC800 when processed at 500 and 800oC, respectively. The nomenclature uses “MG” because

this material comes from a digester using ferric chloride (FeCl3) to precipitate phosphorous as part

32

of a manure management study. The pyrolyzed digestate was qualitatively determined to be

magnetic, consistent with prior research of our group (Rodriguez Alberto et al., 2019). Similarly,

DMBC500 and DMBC800 identified dry manure biochar, and FWBC500 and FWBC800

identified mixed food waste biochar, produced at both 500 and 800 ºC.

Figure 2.1 - Microwave furnace for biochar production under oxygen-free (pyrolysis) conditions

33

2.2.3 Surface area and pore size measurements

The NOVAe Series Model 4200 (Figure 2.2) was procured from Quantachrome Instruments,

currently owned by Anton Paar. This model has four analysis stations that allow for the

determination of surface area, pore size and pore radius.

Figure 2.2 - Quantachrome NOVAe system for surface area and pore size measurement

The instrument offers a relatively rapid measurement and has the capacity to use both nitrogen and

carbon dioxide to perform the analysis. The NOVAe series also allows for the degassing of the

material to be studied and uses the Brunauer-Emmett-Teller (BET) theory to study the physical

adsorption of gas molecules.

34

To perform this analysis, approximately 0.2 g of biochar was placed in a glass cell and degassed

for 24 hours at 105 ºC. The degassed samples were then placed in the analysis stations of the

Quantachrome instrument. The surface area, pore size of desorption and pore radius were

measured based on the BET theory with N2 as a medium. The data were logged and stored

electronically, and the absorption and desorption graphs are provided in Appendix A. This analysis

was done in four replicas for each biochar sample.

2.3 Results and Discussion

The results of the characterization experiments for the six biochar materials produced from dry

manure, food waste and digestate (DMBC500, DMBC800, FWBC500, FWBC800, MGBC500,

MGBC800) include measurements of yield, pH, surface area, mean pore volume, mean pore

surface area, and mean pore radius (Table 2.1 and Figure 2.3).

2.3.1. Biochar yield

Higher yields often indicate an elevated value of ash content in the biochar because higher

temperature biochar has a higher ratio of inorganic materials. Lower processing temperatures cause

minimal condensation of aliphatic compounds and lower losses of CH4, H2, and CO. Conversely,

higher temperatures promote dehydration of hydroxyl groups and thermal degradation (Novak et

al., 2009).

Factors such as temperature, biomass source, and holding time influence biochar yield, as does

material density. All biochar samples followed the expected trend, with higher temperatures

resulting in lower yield (Table 2.1). Biochar processed at higher temperatures resulted in a lower

yield than those processed at 500 ºC, and this can be attributed to the complete carbonization of

35

the feedstock material. The material is not always completely converted to biochar when processed

at 500 ºC (Demirbas, 2004) which would explain the higher yields on biochar at this temperature.

Magnetic biochar derived from digestate was found to have the highest yield among all the

biochars produced, 48.73 % for MGBC800 and 62.00 % for MGBC800. This result is attributed

to the higher density created when treating the digestate with ferric chloride to extract the

phosphate in the sample. The yields for DMBC and FWBC were within the normal range expected

for biochar, 31.48% for DMBC500, 29.05% for DMBC800, 33.53% for FWBC500, and 28.20%

for FWBC800.

2.3.2. Biochar alkalinity

The pyrolysis of biomass has been shown to affect pH, resulting in increases in alkalinity and

changes in ash content. Higher pyrolysis temperature results in an increase of surface area,

carbonized fractions, pH and volatile matter, and a decrease of cation exchange capacity (CEC)

and content of surface functional groups (Tomczyk et al., 2020). A study by Cantrell et al. (2012)

showed that biochar from dry manure had a higher pH with increased pyrolysis temperature, also

confirmed in the present study (Table 2.1). Among all the results, biochar produced from food

waste at 500 ºC had lowest pH. The results can be attributed to the feedstock source itself, since

food waste is rich in cellulose and other sugars, and the carbonization process allows for a lower

pH. In the case of dry manure feedstock, the resulting biochar has a pH of 9.66 when processed at

500 ºC and 11.64 at 800 ºC. It can be said that the results are due to the separation of salts, calcite

and quartz which are attached to the hemicellulose of the manure (Cao & Harris, 2010).

36

Among all biochar samples, the highest pH was found in the digestate biochar, MGBC. Since this

biomass was pretreated with ferric chloride, it has a higher level of alkali salts which increased in

concentration as the carbonization of the material increased. The pyrolysis process increases the

ash concentration in biochar, which would also explain the relatively high pH.

2.3.3. Surface area and pore size analysis

Pyrolysis temperature has an effect on the physicochemical characteristics of biochar, impacting

pore size and surface area in the same way as it does pH. Processing temperature and biomass

sources can determine appropriate potential biochar applications (Ding et al., 2014; Tomczyk et

al., 2020). After pyrolysis, there are more cracks of the compounds present in the surface of the

biochar which increases pore depth, due to pore blocking substances being driven off by increasing

temperature. These compounds are thermally cracked, and pores are formed thus increasing the

surface area while decreasing particle size (Rafiq et al., 2016; Tomczyk et al., 2020). The presence

of amorphous carbon structure increases with temperature and cellulose containing biochar might

be better at capturing aromatic compounds and acting as better adsorbents (Tomczyk et al., 2020).

Figure 2.3 shows the results of BET analysis of each biochar. MGBC has the highest surface area

and pore volume, which can be attributed to smaller metal particles that are attached to the surface

of the biochar during the pretreatment of the digestate. There is a direct relationship between the

increase in pyrolysis temperature and the increase of surface area. The lowest surface area was

found on FWBC500 with 2.43 m2/g, followed by 3.28 m2/g for DMBC500, 6.31 m2/g for

MGBC500, 6.38 m2/g for FWBC800, 8.98 m2/g for DMBC800, and 98.83 m2/g for MGBC800.

The results show an increase in surface area and pore size with temperature, however with the

exception of MGBC800, all the biochar have a relatively low surface area compared to many of

37

the prior literature studies (Table 1.1). Because the BET analysis was performed with N2 gas

instead of a smaller gas molecule such as CO2, it is hypothesized that the surface area analysis was

not comprehensive enough since N2 cannot enter micro- and nano-pores (Weber and Quicker,

2018). A more comprehensive analysis, that fully interrogates pores of all sizes, can be performed

using CO2 or highly wetting liquids like butane.

Table 2.1 - Yields and characterization data of biochar samples derived from various feedstocks

processed at 500 and 800 ºC

Name Yield

(%) pH Surface area

(m2/g) Mean pore

volume (cm3/g) Mean surface

area of

desorption (m2/g)

Mean pore

radius (nm)

DMBC500 31.48 9.66 3.28 0.0040 2.77 2.02

DMBC800 29.05 11.54 8.98 0.0043 2.58 2.02

FWBC500 33.53 8.94 2.43 0.0033 2.05 2.46

FWBC800 28.20 10.24 6.38 0.0040 2.79 2.01

MGBC500 62.00 10.65 6.31 0.0085 5.80 2.04

MGBC800 48.73 12.10 98.83 0.0270 19.62 2.04

38

(a)

(b)

(c)

Figure 2.3 - Results from the BET analysis: (a) surface area, (b) mean pore volume, and

(c) mean pore radius.

8.983.28 6.38 2.43

98.83

6.31

0

20

40

60

80

100

120

Surf

ace

Are

a m

2 /g

0.004 0.004 0.004 0.003

0.027

0.009

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Mea

n P

ore

Vo

lum

e (c

m3 /

g)

20.21 20.24 20.15

24.59

20.40 20.37

0

5

10

15

20

25

30

Mea

n P

ore

Rad

ius

(Å)

39

CHAPTER 3

EFFECT OF BIOCHAR ON BIOMETHANE PRODUCTION VIA

ANAEROBIC DIGESTION

3.1 Introduction

As highlighted in Chapter 1, there is a need to understand the characteristics that enable biochar to

become useful as an adsorbent in the anaerobic digestion (AD) process. This chapter focuses on

the effects that adding different biochar has on the production and stability of AD. Based on the

extensive literature summarized in Table 1.1, it has been demonstrated that the addition of

carbonaceous adsorbents (including biochar) may have an impact on the productivity of AD

systems, in regards to biogas quality, biomethane production kinetics and maximum yield, as well

as shortening the lag time of the hydrolysis reaction. It is expected that biochar can act as a buffer

and promote bacterial reproduction, while at the same time provide space for the bacteria to form

clusters and have better access to the substrate. In this chapter, results of biomethane potential

(BMP) experiments are presented using in-house biochar materials produced at two temperatures

from three different feedstock sources (Chapter 2).

3.2 Methods

3.2.1 Inoculum and substrate preparation

Inoculum was obtained from Synergy LLC, a commercial-scale anaerobic digester located in

Covington, Wyoming County, NY. The inoculum was degassed at 37ºC for five days to ensure

that all available nutrients from the previous process had all been sufficiently degraded. The

substrate used in these experiments was a 10% TS Purina Beneful ® dog food semi-solid solution.

This material was selected as a model mixed food waste substrate that would offer consistent

40

composition throughout the experimental campaign, a requirement that would have been difficult

to maintain using our own mix of food waste which can vary considerably. The nutritional value

of the selected substrate is provided in Table 3.1. The pellets were mixed with deionized (DI) water

in a Vitamix blender until completely homogenized.

Table 3.1- Purina Beneful ® nutritional content as indicated on the product package

Component Mass Content

Protein 25.0%

Fat 8.0%

Fiber 9.0%

Moisture 14%

Linoleic Acid 1.2%

Calcium (Ca) 1%

Selenium (Se) 0.35 mg/kg

Vitamin A 10,000 IU/kg

Vitamin E 100 IU/kg

3.2.2 Total and volatile solids determination

Total solids (TS) and volatile solids (VS) measurements were performed as directed in the AMPTS

II start-up guide (Bioprocess Control, 2016). Clean and dry crucibles were used to weigh the

substrate and then placed in a furnace at 120ºC for 20 hours. Afterwards, the samples were

removed from the oven and placed in a desiccator until they cooled down. The crucible and dried

samples were weighed to calculate the total solids contained in the sample. To determine volatile

solids, the dried samples were then placed in a high temperature furnace at 550ºC for 2 hours and

weighed again once they reached room temperature. Equations 3.1 and 3.2 show the calculations.

𝑇𝑜𝑡𝑎𝑙 𝑆𝑜𝑙𝑖𝑑𝑠 [%𝑤] =𝑤𝑊𝑒𝑡

𝑤𝐷𝑟𝑦× 10 [Equation 3.1]

41

𝑉𝑜𝑙𝑎𝑡𝑖𝑙𝑒 𝑆𝑜𝑙𝑖𝑑𝑠[%𝑤] =𝑤𝐷𝑟𝑦−𝑤𝐴𝑠ℎ

𝑤𝐷𝑟𝑦× 100 [Equation 3.2]

3.2.3 Automatic Methane Potential Test System II (AMPTS II)

The AMPTS II system, shown in Figure 3.1, was procured from Biomass Controls (Lund,

Sweden). This instrument is the latest technology on automated data collection for batch anaerobic

digestion systems. Each 500 mL glass bottle represented an independent reactor inoculated in an

anaerobic environment and placed in a constant-temperature water bath. The biogas produced in

each bottle then passed through a 4.0 M sodium hydroxide (NaOH) solution that sequesters the

CO2. A gas detector then calculated the cumulative amount of biomethane (CH4) produced over a

given time.

Figure 3.1 – (left) AMPTS II system for biomethane potential (BMP) measurements

(right) Sample bottles; 30 total bottles in separate water baths, each accommodating 15 bottles

42

For reactor start-up, biochar loadings of 0.5, 1, and 2 w/w% were mixed with the dog food substrate

and inoculum in 500 mL bottles with a 200 mL headspace. Each reactor had an automated agitator

running at 60 rpm that mixed the contents for 10 seconds every 60 seconds. The reactors all had a

2:1 inoculum-to-substrate (I/S) ratio and were prepared based on volatile solids (VS) amounts. The

bottles were placed in two water baths controlled at 37ºC and connected into the system where the

gas produced would pass through NaOH solution to eliminate CO2 from the biogas. The system

was first purged with N2 and then data collection started. Each run took 30 days to be completed

and data analysis was conducted at the end of each experimental cycle. Equation 3.3 outlines the

calculation done to determine the BMP for each reactor (an example of this calculation can be

found in Appendix B.5):

𝐵𝑀𝑃 [𝑚𝐿

𝑔𝑉𝑠] =

𝑉𝑠−𝑉𝑏 ×(𝑚𝐼𝑠𝑚𝐼𝑏

)

𝑚𝑆𝑠,𝑉𝑠

[Equation 3.3]

where

BMP = biomethane potential, the normalized volume of methane produced per gram of volatile

solids (NmL/gVS)

Vs = cumulative volume of methane produced from the reactor with the sample (NmL)

Vb = mean value of cumulative volume of methane produced by the three blanks (NmL)

mIs = total amount of inoculum in the sample (g)

mIb = total amount of inoculum in the blank (g)

mVS,Ss = amount of organic material of substrate contained in the sample bottle (gVS).

43

An example of the raw output from the AMPTS II system is provided in Figure 3.2, for one of the

samples run with pure dog food (i.e., without added biochar). As can be seen, for this substrate

material rich in proteins and carbohydrates, methane production begins very rapidly with a short

lag time. Also, most of the methane production (774 mL) occurs in the first 10 days, whereas only

an additional 54 mL is generated between days 11 and 30. To compute the final BMP value

according to Equation 3, the cumulative amount of methane generated after 30 days (in this case,

828 mL) was normalized by first subtracting the mean amount of methane produced by the blanks

(i.e., inoculum only). Then, this value was corrected for the difference in inoculum mass between

the sample and the blank, and then divided by the mass of organic material (in grams volatile

solids) present in the sample bottle.

Figure 3.2 – Example of raw methane volume data generated by AMPTS II system during

mesophilic digestion of food waste

44

3.2.4 Stress simulation run

To simulate an anaerobic digestion process operating under stressed conditions (by increased

organic loading), a similar BMP experiment was performed. The reactor start-up was conducted

using the highest performing biochars identified in the experiments described in Section 3.2.3:

MGBC500:2%, MGBC800:0.5%, DMBC500:0.5%, DMBC800:0.5%, FWBC500:1%, and

FWBC800:2%. The biochar was loaded into the 500 ml bottles, allowing for a 200 mL head space.

Each reactor had an automated agitation at 60 rpm that mixed the contents for 10 sec every 60 sec.

The reactors had I/S ratio of 1:1 for the experimental reactors and 2:1 for the control group. The

reactors were run until the biogas production rate dropped to 2 mL/day.


3.3.1 Food waste biochar

Figure 3.3 shows the biomethane potential (BMP) results for the two food waste biochar samples,

FWBC500 and FWBC800. The highest BMP obtained during this run was from the addition of

FWBC500 with a 1% loading of biochar. This resulted in 410.2 mL CH4/gVS, which amounts to

an increase of 11.8% when compared to 367.1 mL CH4/gVS from the control group (i.e., dog food

only). FWBC500 showed an optimal BMP at 1%1, while the lowest was at 2% loading with 368.3

mL CH4/gVS. In the case of FWBC800, the highest BMP was found to be with a 2% loading

which amounted to a 7.2% difference when compared to the control. Between the two biochar

samples at their optimal loading levels, there was a difference of 4.7%. The results are highly

influenced by the specific characteristics and composition of the two biochar samples. Various

factors could be at play that will aid in the understanding of this behavior.

1 This and all subsequent loading values are weight percentages.

45

Figure 3.3 - (a) Biomethane potential and (b) percent difference results (relative to pure dog food)

obtained from the run performed using food waste biochars (FWBC500 and FWBC800). These

results were taken from data on Day 30 of the experiment. The error bars represent the calculated

standard deviation within each triplicate set.

46

The characterization data presented in Chapter 2 showed that the lowest pH was found at lower

processing temperatures. In this case, FWBC500 has the lowest pH among all the biochar samples.

Since the biochar substrate is similar in composition to the substrate during AD, there is a more

direct relationship which allows for a better buffering capacity in the reactor. In this case the

temperature of processing of the biochar did not have the expected results. The higher surface area

and pore size was achieved at 800 ºC, however, the highest BMP was found from a biochar with

the lower processing temperatures.

3.3.2 Dry manure biochar

Dry manure was the most consistent feedstock obtained for conversion to biochar. The material

was dried prior to processing which allowed for the extraction of moisture enclosed within the

surface of the substrate and can explain the increase in surface area of this biochar once converted.

The maximum BMP obtained for these experiments was with DMBC500 with a loading of 0.5%

(Figure 3.4). The BMP for that specific biochar loading was 427.6 mL CH4/gVS, and accounted

for a difference of 9.4% in comparison to the control group (391 mL CH4/gVS) for the run.

DMBC800 biochar samples followed a trend in which higher biochar loadings decreased the BMP.

In the case of DMBC500, however, there was not a clear trend with increased biochar loadings.

These results again can be explained by looking at the pH results. Lower alkalinity is found at

lower temperature which explains why somewhat higher BMP values were attained with

DMBC500. The AD process needs to maintain a near-neutral pH of 7-8. Since biochar acts as a

47

buffer, it needs to provide adsorbent qualities while not disrupting the system altogether by

introducing relatively high or low pH that may have a negative effect on the microbial community.


obtained from the run performed using dry manure biochars (DMBC500 and DMBC800). These

results were taken from data on Day 30 of the experiment. The error bars represent the calculated

standard deviation within each triplicate set.

48

3.3.3 Digestate biochar

Digestate biochar was derived from the effluent of an anaerobic digester treated with ferric chloride

(FeCl3) to recover phosphorous for re-use. As shown by Rodriguez Alberto et al. (2019) and others,

during the pyrolysis process these iron-containing compounds can be converted to magnetite

(Fe3O4), thus imparting magnetic properties to the biochar. The digestate biochar produced for this

research was indeed confirmed to be magnetic. This was demonstrated by using a handheld magnet

and qualitatively observing the biochar’s attraction to it. Based on recent literature (Table 1.1),

this trait was expected to increase the capacity of this specific biochar to increase BMP during AD.

However, the result showed similar results as previous runs (Figure 3.5). The increase in BMP was

highest at around 10.83% for MGBC500 with a 2% difference compared to dog food which

amounts to a BMP of 370 mL CH4/gVS. There is no clear trend for MGBC500 with an increase in

biochar loading. In the case of MGBC800, the BMP results remained within close range of each

other. The lowest BMP for that biochar was 334 mL CH4/gVS and the highest was 340 mL

CH4/gVS. At 800ºC, the MGBC showed the highest pH, and surface area results. Previous research

has determined that higher surface area will have a higher impact on BMP (Ye et al., 2018),

however, higher pH in the biochar will tend to offset the buffering capacity that the higher surface

area provides (Du et al., 2020). This implies that even when a small increase in BMP is observed,

it may still maintain a stable production of biogas.

To further understand the results there is a need to perform more in-depth analyses of each biochar

sample, to better understand how the composition of each biochar is enhancing the stability of the

system. The stressed conditions experiments described in the next section hope to shed light into

the stabilizing effect that each biochar has when added to the AD process.

49


obtained from the run performed using magnetic digestate biochar (MGBC500 and MGBC800).

These results were taken from data on Day 30 of the experiment. The error bars represent the

calculated standard deviation within each triplicate set.

50

Figure 3.6 – Percent difference in ascending order for each run and biochar loading.

3.3.4 Stressed condition run with digestate biochar

A number of the previous studies summarized in Table 1.1 have shown biochar to have a

stabilizing influence when added to AD. This experiment was designed to understand the effect

that doubling the volatile solids present in the system would have. This system change provided

the bacteria with a higher amount of organic material in the system, which would be expected to

lower the pH. After 15 days of this run, the experiment had to be stopped due to laboratory access

issues.

When comparing the two dog food (DF) control groups, the run which had double the volatile

solids added showed to have more than doubled the amount of biomethane produced. The DF run

with an I/S ratio of 2:1 produced 198.03 mL CH4/gVS, while the one with a ratio of 1:1 resulted

in 433.57 mL CH4/gVS (Figure 3.6). This is understandable because when doubling the amount

-2%

0%

2%

4%

6%

8%

10%

12%

14%B

MP

dif

fere

nce

(%

)

51

of volatile solids present, the bacteria will have better access to the substrate which means more

will be digested.

When adding the biochar samples into the run, there was not a big difference compared to the

control group which had the same I/S ratio. This means that the biochar does stabilize the system

but does not provide the same value as it does when using a lower ratio of feed. It is important to

also note that since this run only lasted 15 days, it can be said that adding biochar to the system

can potentially triple the quantity of volatile solids which means more food waste can enter the

system.

It is important to further study the degree to which the addition of more food waste into the AD

system can be achieved, since higher organic loading rates can become problematic in the long

run. In this case, however, it seems that the food waste provides the needed nutrients to make the

system work sufficiently. This means that the use of a “lesser” substrate such as chicken manure

may show different results.

52

Figure 3.7 - (a) Biomethane potential results obtained from the run with the best performing

biochar. These results were taken from data on Day 15 of the experiment.

The extensive results in this chapter show the effects of adding various biochar types into different

anaerobic digesters. The effects specifically focused on the interaction between food waste and

waste from other streams. More research is needed to better understand the optimal process for

using biochar in anaerobic digestion, namely through the study of more combinations of substrates

and biochar types.

The results of Chapter 3 experiments showed generally small enhancements in biomethane

potential, regardless of the type of biochar material and mass loading employed. For all results

presented in Figures 3.3 to 3.6, the BMP enhancement relative to the dog food-only baseline ranged

from -0.1% for 1% magnetic biochar made at 800 ºC (MGBC800), to +11.8% for food waste

biochar made at 500oC (FWBC500). There is a possibility that the biochar only had a small effect

200.61 198.03

433.57 431.37451.37 439.58 453.62 446.24

360.32

0

100

200

300

400

500

600

BM

P (

mL

CH

4/g

VSs

)

53

on the AD of dog food because this substrate contains a good amount of degradable material and

its ingredients are well balanced. In future research, there is a possibility to explore a substrate

which has proven unstable conditions and low BMP. The addition of biochar can play a role in

lowering the amount of system shutdowns done when there is an offset in the AD productivity.

This would mean lower costs and more diverse substrates can be added to the system which would

increase value.

In these experiments, biochar samples that were made at lower temperature showed an increase in

BMP of around 10% on average with FWBC500 with 0.5% loading being the highest at 11.73%.

This experiment proved that biochar alkalinity in this case plays a bigger role than surface area.

AD is a very sensitive system and the addition of biochar appears to help stabilize the process,

potentially increasing the overall economic value of AD.

54

CHAPTER 4

TECHNO-ECONOMIC ANALYSIS OF BIOCHAR ADDDITION IN

ANAEROBIC DIGESTION

4.1 Introduction

The previous chapters focused on a comprehensive literature review of biochar augmentation of

anaerobic digestion, the in-house characterization of six different biochar samples, and their effect

on the anaerobic digestion process for a model food waste substrate. The research and data

collected shed light onto the relationship between biochar characteristics and a resulting increase

in biomethane potential (BMP), that could translate into meaningful economic value for an

anaerobic digester (AD) system developer. These systems could attain improved profitability with

the right combination of biochar feedstock, pyrolysis process parameters, and digested substrate.

This chapter focuses on quantifying the economics of biochar addition to working AD systems.

The study was conducted by modeling a working AD system in the Upstate New York region, the

subject of previous publications by our research group (Ebner et al., 2015). This facility is co-

located with a large dairy farm managing over 1900 cows that generate manure pumped into the

AD system, in addition to food waste from various commercial generators, mostly food processing

plants. This AD system has been operating since 2012 and has an electrical generator with

nameplate capacity of 1.4 MW. It sequesters around 7700 t CO2 eq. annually and accepts around

1.14 million gallons of food waste per year (CH4 Biogas, 2012). The facility has a system that

collects and logs various data on their digester operation and processed feedstocks. This

information and data from other sources were used to simulate various scenarios discussed in detail

below. The economic analysis is a matter of assessing the costs of producing or procuring biochar,

55

and the equipment needed to add the biochar to the AD system, versus the value of five potential

sources of revenue: additional electrical energy production, additional thermal energy production,

increased tipping fees from accepting more food waste, renewable energy credits (RECs) and

carbon credits.

4.2 Methods

4.2.1 Capital and operation and maintenance (O&M) costs

Capital cost (CAPEX) was considered for all scenarios described below, but only for purchases

associated with adding the capability for biochar addition; the cost of the AD system itself was not

included. Because the modeled anaerobic digester would have already been operating without

biochar, none of the regular O&M and capital costs of the baseline AD system were included in

the analysis. There have been previous economic studies reporting that the capital cost of a new

biochar-producing pyrolysis system is dependent on the amount of waste to be processed, with the

average for commercially-available systems estimated at $70 per metric ton2 of material processed

per year (Dickinson et al., 2015). For much smaller systems, such as that which would be deployed

at the scale of an individual farm, this cost factor is about $200/t. The CAPEX of the pyrolysis

system for our model was calculated based on the $200/t factor, multiplied by the amount of

biochar needed to provide 1% loading on a yearly basis, assuming a yield of 33% by weight. For

the other scenarios in which the biochar is procured from a third party, the prices were estimated

as low, mid, and high, and are reported along with relevant capital and O&M costs in Table 4.1.

In each case, the underlying assumption or basis is also included. The remaining data used as inputs

for the net present value computation described below are summarized in Tables 4.2 through 4.4.

2 Throughout this chapter, the symbol “t” is used to indicate metric ton, equivalent to 1000 kg.

56

The addition of pyrolysis biochar into a working anaerobic digester will also require the

installation of an additional piece of equipment that can efficiently add the biochar material

upstream of the AD reactor into a batch mixer, currently used to pre-blend the food waste and

manure streams. Based on information obtained directly from the AD system operator, and other

sources of chemical process equipment costs (Towler and Sinnott, 2012), it was assumed that a

capital investment of $50,000 would be needed for equipment to support integrated biochar

storage, handling and metering into the batch mixer. This estimate is based on the cost correlation

provided for a 0.5 m wide belt conveyor with 5 m length. As described in the analysis presented

below, the net present value results are not strongly influenced by the assumed cost of the biochar

equipment, even if increased by a factor of two.

Table 4.1 – NPV model inputs related to biochar equipment and materials, assuming baseline

food waste input in modeled AD plant

Parameter Value Assumption / Source

Amount of biochar needed 573 t/yr

1% biochar loading, based on total feedstock mass

processed at local AD plant in 2019 (manure +

food waste).

Biochar material (low) $50/t 25% of the baseline (mid) cost

Biochar material (mid) $200/t Baseline cost at nominal processing capacity of

100,000 dry t/year (Dickinson et al., 2015)

Biochar material (high) $1,000/t 5X of baseline (mid) cost

CAPEX of pyrolysis system $347,000 $200 per metric ton feedstock processed per year

(Dickinson et al., 2015)

O&M cost of pyrolysis system $7000/yr 2% of CAPEX (Win et al., 2017; Aui and Wright,

2018)

CAPEX of equipment for

biochar metering $50,000 Towler and Sinnott (2012)

O&M cost of pyrolysis system $1000/yr 2% of CAPEX (Win et al., 2017; Aui and Wright,

2018)

57

Table 4.2 – NPV model inputs related to anaerobic digester equipment and materials, assuming

baseline food waste input in modeled AD plant


Biogas production rate 3,940,672 m3/yr AD plant operation data (2019)

Methane content in biogas 60% In-house laboratory data

Annual food waste processed 11,472,974 gal/yr AD plant operation data (2019)

Annual dairy manure processed 2,958,404 gal/yr AD plant operation data (2019)

Specific energy of CH4 50.0 MJ/kg Assumed

Gen-set electrical efficiency 30% Win et al. (2017)

Gen-set thermal efficiency 50% Win et al. (2017)

Table 4.3 – NPV model inputs related to financial parameters


Carbon

credits

$13/ MT ton

CO2 eq. Perez Garcia (2014)

Wholesale

natural gas

price

$2.56/MMBtu www.eia.gov/outlooks/steo/report/WinterFuels.php

Wholesale

electricity

price

$0.03/kWh USDA (2007)

Electricity

price $0.06/kWh

www.eia.gov/electricity/monthly/epm_table_grapher.php?t=ep

mt_5_6_a

Tipping

fees $52.62/t EREF (2019)

Maturity

date 20 yr Assumed life of AD plant

2020 US

discount

rate

2.5 % ycharts.com/indicators/us_discount_rate

Table 4.4 - Conversion factors used in NPV calculations

Parameter Value Unit

kWh to Btu 3412 Btu/kWh

Heating value of methane 55.6 MJ/kg

Btu to therm 1.00E-05 therm/Btu

MJ to kWh 0.2778 kWh/MJ

Tons per kg 1000 kg/ton

Electricity yield 0.448 kg CO2/kWh

gal to ton 31.75 gal/ton

http://www.eia.gov/outlooks/steo/report/WinterFuels.php

http://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a

http://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a

https://erefdn.org/wp-content/uploads/2017/12/MSWLF-Tipping-Fees-2018-Rev.ed_.2019.pdf

https://ycharts.com/indicators/us_discount_rate

58

Based on the detailed empirical results presented in Chapter 3, the economic model is based on

the assumption that 1% biochar addition (based on the total mass of food waste + manure in the

baseline AD system) produces an additional 10% methane relative to the baseline system without

biochar.

4.2.2 Revenue from electrical and thermal energy generation

Calculations to determine electricity generation and the associated energy savings followed the

method used by Win et al. (2017). Biogas from AD systems can be directly combusted in a boiler

to generate a hot water supply. However, consistent with the system architecture of the modeled

AD plant, it was assumed that the biogas is combusted in an engine-generator set (gen-set) to

produce electricity that is put onto the grid with a value of $0.03/kWh (Table 4.3). The waste heat

from the gen-set is recovered through the cooling water jacket of the gen-set, and all of this thermal

energy is used on-site. The value of this thermal energy was thus computed based on the cost of

natural gas that would have otherwise been purchased ($2.56/MM Btu). These factors allowed for

the calculation of electricity generation (EG) and waste heat generation (HG) as shown in

equations 4.1 through 4.3. The direct use of biogas was calculated using Equations 4.1 and 4.2.

EG(MWh/𝑦𝑟) = BMP × CV × ƞ𝑒𝑙 [Equation 4.1]

HG (BTU/yr) = BMP × CV × ƞ𝑏𝑙 [Equation 4.2]

59

where:

BMP = biomethane production per year (m3 CH4/ yr)

CV = calorific value (MJ/m3 CH4)

Ƞel = gen-set electrical conversion efficiency (%)

Ƞth = gen-set thermal conversion efficiency (%)

After calculation of EG and HG, the income was calculated using the current average wholesale

prices for natural gas in the case of HG and electricity in the case of EG (Table 4.3).

4.2.3 Revenue from tipping fees

The modeled Upstate New York AD plant was used to determine specific loading of food waste

into the digester. The quantity of waste was calculated for each scenario taking into account an

increased loading of food waste of 1, 5, 10 and 20 weight% greater than the baseline system,

assumed to be enabled by the stabilizing effect of adding 1% by weight of biochar to the total

amount of food waste and manure being processed. The tipping cost of $52.62/ton shown in Table

4.3 was obtained from the 2019 average U.S. landfill tipping costs. It is assumed that food waste

generators would be motivated to direct waste to the AD plant instead of the landfill if there is not

an economic penalty to do so.

4.2.4 Revenue from renewable energy credits (RECs)

The direct benefits of biochar addition are expected to emanate from enhanced biomethane

production, which enables the AD system to generate more electrical and thermal energy;

furthermore, stabilizing the biochemical process allows for additional digestion of food waste that

60

would otherwise not be processed and most likely sent to landfill. Because anaerobic digestion is

considered a sustainable energy technology that displaces fossil fuel-derived energy, there are also

opportunities for government-sponsored incentives to improve AD competitiveness versus

incumbent energy technologies. Renewable energy credits were calculated using NYSERDA’s

anaerobic digester gas-to-electricity incentives, based on the Customer-Sited Tier (CST) program

which supports the operation and installation of anaerobic digesters (Enahoro and Gloy, 2008). In

this case, only the ongoing income was taken into consideration since the AD system was already

built prior to the addition of biochar. The calculations were performed as reported by Win et al.

(2017).

4.2.5 Revenue from carbon credit

Anaerobic digestion also qualifies for carbon credits because it avoids greenhouse gas generation

by sequestering carbon from the waste being processed. The same analysis as Win et al. (2017)

was performed to quantify the carbon credit benefit. Briefly, values for 10% biogas production

were calculated for each scenario, and a carbon mitigation value of $13/t CO2 eq. was applied.

Carbon credits were calculated using equation 4.3:

𝐶𝑎𝑟𝑏𝑜𝑛 𝐶𝑟𝑒𝑑𝑖𝑡𝑠 = 𝐵𝑀𝑃 × 𝐶𝑉 × ƞ𝑏𝑙 × 𝐶𝐹 × 𝑂𝑃 [Equation 4.3]

where:

BMP = biomethane production per year (m3 CH4/ yr)

CV = calorific value (MJ/ m3 CH4)

CF = conversion factor (kWh/m3 CH4), (BTU/kWh), (therm/BTU)

Ƞth = gen-set thermal conversion efficiency (%)

61

OP = carbon offset price ($/t CO2 eq.)

4.2.6 Net Present Value (NPV) model

The Net Present Value (NPV) was used to determine the financial viability of 4 scenarios:

procuring a pyrolysis system to produce biochar on-site (Scenario 1), and procuring biochar based

on low, mid and high prices of $50, $200 and $1000/t, respectively (Scenarios 2-4). Equipment

lifetime was only considered for the procured biochar addition equipment and pyrolysis system,

and it was assumed that the AD system would be working for 20 years from the first time biochar

was added to the system. The NPV was calculated taking into consideration that the addition of

more food waste into the system would increase the biochar addition requirement, tipping fees,

and the enhanced methane generation would remain as 10% of the methane that would have been

generated from the total food waste + manure without biochar. NPV was calculated in 2020 US

dollars, and cash flow was determined for each scenario depending on specific characteristics:

𝑁𝑃𝑉 = −𝐼 + ∑𝐶𝐹𝑡

(1+𝑖)𝑡𝑇𝑡=1 [Equation 4.5]

where:

I = initial capital investment (for biochar metering equipment, and also pyrolysis system

for Scenario 1)

CFt = cash flow (revenue – cost) for each year t

I = discount rate = 2.5% (Table 4.3)

t = year

62


Economic analysis for each of the four scenarios was conducted to understand the value of adding

biochar. Previous chapters revealed there is a relationship between biochar addition and an

increase in stability of the system. Also, by adding biochar there is a possibility of increased value

by the acceptance of higher quantities of food waste and possibly diversifying the substrates able

to be used.

Figure 4.1 presents the results of the techno-economic analysis based on the conservative

assumption that no government incentives are available, and the financial viability of biochar

addition is based entirely on enhanced electrical and thermal energy generation and increased

tipping fees. Several interesting trends emerge. First, without incentives, the high biochar cost of

$1000/t (Scenario 4) makes the NPV negative regardless of how much additional food waste can

be utilized as a result of the stabilizing influence of biochar. The other three scenarios all show

conditions under which the addition of biochar may be a sound financial decision. In the case of

buying a pyrolysis system for on-site biochar production (Scenario 1), positive NPV is achieved

with as little as 1% additional food waste relative to the baseline AD system. However, for all

cases without government incentives, some cash flow from food waste tipping fees is required to

achieve positive NPV, and financial viability cannot be achieved by relying solely on the value of

additional electrical and thermal energy production. It is also important to note that procuring

pyrolysis equipment (Scenario 1) yields economic outcomes that are essentially equivalent to

procuring low cost biochar at $50/t (Scenario 2). This result may motivate an AD system operator

to consider purchasing on-site pyrolysis equipment, because maintaining a consistent, high-quality

biochar supply at $50/t over the assumed 20 year plant life may be difficult, and to our knowledge

63

is not practical in light of the existing biochar market and supply chain, at least in the U.S. Adding

the incentives of renewable energy credits (RECs) and carbon credits as additional cash flows has

the expected effect of making all four scenarios more favorable for investment (Figure 4.2). Only

the case of high biochar price (Scenario 4) yields negative or near-zero NPV, while all other

scenarios achieve financial viability even without the cash flow from tipping fees (0% added food

waste). Again, the outcomes from purchasing pyrolysis equipment (Scenario 1) and buying low-

cost biochar (Scenario 2) are nearly equivalent.

Even though the results presented in Figures 4.1 and 4.2 show many situations under which the

computed net present value is positive, this does not immediately mean that the project is worthy

of investment. A plant manager needs to decide if the projected rate of return is better than the

potential benefit from investing available funds in other capital improvements, new products, etc.

To help support this decision process, it is useful to determine the internal rate of return (IRR),

which is the discount rate at which the NPV becomes zero. If the IRR is high relative to the

projected return of other options, then the project may be a worthwhile investment.

The internal rate of return was computed for the case of buying pyrolysis equipment (Scenario 1)

with an assumed increased food waste supply of 5%. Because there is significant uncertainty

associated with the CAPEX of on-site pyrolysis equipment and the exact requirements of the

equipment needed for biochar addition, for the IRR analysis the capital costs were assumed to be

twice those used in the main analysis: biochar equipment cost increased from $50,000 to $100,000,

and $347,000 to $694,000 for the pyrolysis equipment. The results shown in Figure 4.3

demonstrate that the internal rate of return under these conditions is 16%, a reasonably attractive

64

value for a 20-year project. However, it should be stressed that this result is strongly dependent on

the assumed level of additional food waste that can be introduced to the anaerobic digester as a

result of biochar’s stabilizing influence. For example, with 1% additional food waste, the net

present value at the higher assumed equipment CAPEX is negative, even at 0% discount rate.

Figure 4.1 – No-Incentive Case: Net Present Value (NPV) for the addition of pyrolysis biochar to

a working AD system, including purchased pyrolysis system for biochar production and

low/mid/high costs of purchased biochar. The impact of increasing food waste processing of 1, 5,

10 and 20% of the baseline are indicated. In this case, incentives (renewable energy credits and

carbon credits) are not included in the annual cash flow.

$(0.19) $(0.18)

$(1.74)

$(10.07)

$0.28 $0.30

$(1.28)

$(9.67)

$2.20 $2.21

$0.59

$(8.07)

$4.70 $4.71 $3.37

$(3.78)

$9.38 $9.39

$7.58

$(2.06)

$(15.00)

$(10.00)

$(5.00)

$-

$5.00

$10.00

$15.00

Buy System Low Biochar Price Mid Biochar Price High Biochar Price

Ne

t P

rese

nt

Val

ue

(Mill

ion

s)

0% 1% 5% 10% 20%

Additional food waste mass relative to baseline

65

Figure 4.2 – Incentive Case: Net Present Value (NPV) for the addition of pyrolysis biochar to a

working AD system, including purchased pyrolysis system for biochar production and

low/mid/high costs of purchased biochar. The impact of increasing food waste processing of 1, 5,

10 and 20% of the baseline are indicated. Here, the increased revenue from renewable energy

credits (RECs) and carbon credits is included.

$2.16 $2.17

$0.61

$(7.72)

$2.64 $2.65

$1.07

$(7.32)

$4.55 $4.56

$2.94

$(5.72)

$7.06 $7.06

$5.72

$(1.42)

$11.73 $11.74

$9.94

$0.29

$(10.00)

$(5.00)

$-

$5.00

$10.00

$15.00

Buy System Low Biochar Price Mid Biochar Price High Biochar PriceN

et

Pre

sen

t V

alu

e (M

illio

ns)

0% 1% 5% 10% 20%

Additional food waste mass relative to baseline

66

Figure 4.3 – Internal rate of return (IRR) determination for the case of on-site biochar production

with 5% additional food waste. It was assumed that the CAPEX for pyrolysis and biochar addition

equipment was twice that used for the results presented in Figures 4.1 and 4.2, based on a discount

rate of 2.5%

67

CHAPTER 5

CONCLUSIONS AND FUTURE WORK

In Chapter 1 it was demonstrated through a comprehensive literature review that biochar can

benefit anaerobic digestion (AD) processes in a number of ways: increasing the level of

biomethane production, enhancing the quality of generated biogas to achieve higher methane

concentration with fewer contaminants, and increasing system stability to potentially enable

processing of a greater fraction of food waste in co-digestion with animal manure. Despite the

rather extensive body of prior research, only several studies covered AD of food waste under

mesophilic conditions, of particular interest because of the importance of such systems to organic

waste management in Upstate New York. The addition of biochar to the anaerobic digestion (AD)

of food waste was studied to understand the relationship between the addition of adsorbents in the

process and the increase in biomethane potential (BMP). Adsorbents help reduce the presence of

inhibitors, and this is attributed to the pH more so than the surface area. Biochar can help bind

together the bacteria and provide access to the substrate during AD, although pH may play a bigger

part in the upgrading of BMP than expected, even more so than surface area. It was found through

measurements reported in Chapter 2 for biochar derived from food waste, dry manure and digestate

that lower processing temperature during pyrolysis resulted in lower pH, surface area, and pore

size. An example was FWBC500 with 1% loading which had the highest BMP increase at 11.73%.

This biochar had the lowest pH among all other samples.

There are still gaps to be filled due to the lack of information regarding the surface properties of

the biochar samples, and how they can influence fundamental biochemical processes, such as

direct interspecies electron transfer (DIET). In future work, additional characterization including

68

scanning electron microscopy (SEM) and elemental analysis should be performed to determine the

exact composition and morphology of each biochar samples. However, we have a clear

understanding of how pyrolysis temperature influences factors as pH, yield, surface area, and from

this analysis, the potential uses of the biochar as an enhancing additive for AD processes.

The optimal loading of biochar into AD depends on the type of feedstock from which the biochar

was derived. The experimental results reported in Chapter 3 showed that better BMP results are

found between 0.5 to 1% loading. Biochar may be acting as a buffer inside the system which

means that it needs to help maintain the balance in the system and not offset the alkalinity.

However, there is still a need to understand the specific types of biochar which would work best

for each available condition and substrate. More AD experiments can help provide better insight

as to how different stress conditions such as increased levels of inhibitors or extreme pH levels

affect BMP production. Because the experiments in this study were conducted in batch mode,

research into continuous systems would also be needed to evaluate industrial scale applicability.

Literature reported in Table 1.1 reported that thermophilic AD allows for the addition of biochar

to be more effective in the increase of BMP. Future work should compare thermophilic (~55oC)

and mesophilic (~37oC) AD systems as a way to assess the upgrade of biomethane production.

Future work should focus on further understanding how the addition of biochar can help recover a

deteriorated AD system or a system working with substrates which produce low yields of

biomethane. These experiments should be carried out by following a similar experimental design

and replacing the substrates, as done in the current study. Various combinations of substrates can

also be used to determine if the results are similar to the ones obtained in the current study. Other

69

experimentations should also focus on the use of biochar derived from substrates widely available

in our region such as hemp crop residue, cardboard waste, and untreated digestate.

Chapter 4 highlighted the results of the techno-economic analysis (TEA) economic model,

intended to quantify the added value from the enhanced stability proposed by the addition of

biochar to a working industrial scale AD system. It was found that since there is no way for the

anaerobic digesters to control the biochar market price and supply chain, the best choice may be

to build an on-site pyrolysis system which will allow for an increase of up to 10% of the baseline

food waste loading. This economic analysis, however, was based on many assumptions which fit

the model from a local AD system. A future model can be improved in two ways: (1) using all the

economic data from one source or digester without assumptions, and (2) adding more sensitivity

analysis while including the co-digestion data (food waste + manure) within the model. An analysis

of energy consumption and production of a pyrolysis system can shed light to the understanding

of a possible increase in the economic value of building a system. Further work would focus on

the inclusion of the pyrolysis system energy usage and substrate costs since the present study

assumes that the substrate would be available at no cost. The results of the present study show the

potential economic benefit of using biochar in anaerobic digestion, but more research is required

to fully understand how lab-scale results can be translated to commercial scale systems.

70

REFERENCES

Ahmed, I., & Gupta, A. (2010). Pyrolysis and gasification of food waste: Syngas characteristics

and char gasification kinetics. Applied energy, 87(1), 101-108.

Alberto, D. R., Repa, K. S., Hegde, S., Miller, C. W., & Trabold, T. A. (2019). Novel Production

of Magnetite Particles via Thermochemical Processing of Digestate From Manure and

Food Waste. IEEE Magnetics Letters, 10, 1-5.

Appels, L., Baeyens, J., Degrève, J., & Dewil, R. (2008). Principles and potential of the

anaerobic digestion of waste-activated sludge. Progress in energy and combustion

science, 34(6), 755-781.

Aui, A. and Wright, M.M. (2018). Life Cycle Cost Analysis of the Operations of Anaerobic

Digesters in Iowa.

Bioprocess Control (2016). AMPTS II & AMPTS II Light - Automated Methane Potential Test

System: Operation and Maintenance Manual. Version 3.0, June 2016.

Cai, J., He, P., Wang, Y., Shao, L., & Lü, F. (2016). Effects and optimization of the use of

biochar in anaerobic digestion of food wastes. Waste Management & Research, 34(5),

409-416.

Cantrell, K. B., Hunt, P. G., Uchimiya, M., Novak, J. M., & Ro, K. S. (2012). Impact of

pyrolysis temperature and manure source on physicochemical characteristics of biochar.

Bioresource technology, 107, 419-428.

Cao, X., & Harris, W. (2010). Properties of dairy-manure-derived biochar pertinent to its

potential use in remediation. Bioresource technology, 101(14), 5222-5228.

CH4 Biogas (2012), New York's Largest Farm & Food Waste Biogas Facility Opened, Retrieved

from: http://ch4biogas.com/news/synergy-biogas-grand-opening/, April 7th, 2020

Cimon, C., Kadota, P., & Eskicioglu, C. (2020). Effect of biochar and wood ash amendment on

biochemical methane production of wastewater sludge from a temperature phase

anaerobic digestion process. Bioresource technology, 297, 122440.

Cooney, M. J., Lewis, K., Harris, K., Zhang, Q., & Yan, T. (2016). Start-up performance of

biochar packed bed anaerobic digesters. Journal of water process engineering, 9, e7-e13.

71

De Vrieze, J., Devooght, A., Walraedt, D., & Boon, N. (2016). Enrichment of Methanosaetaceae

on carbon felt and biochar during anaerobic digestion of a potassium-rich molasses

stream. Applied microbiology and biotechnology, 100(11), 5177-5187.

Demirbas, A. (2004). Effects of temperature and particle size on bio-char yield from pyrolysis of

agricultural residues. Journal of analytical and applied pyrolysis, 72(2), 243-248.

Dickinson, D., Balduccio, L., Buysse, J., Ronsse, F., Van Huylenbroeck, G. and Prins, W., 2015.

Cost‐benefit analysis of using biochar to improve cereals agriculture. Gcb Bioenergy, 7(4),

pp.850-864.

Ding, W., Dong, X., Ime, I. M., Gao, B., & Ma, L. Q. (2014). Pyrolytic temperatures impact lead

sorption mechanisms by bagasse biochars. Chemosphere, 105, 68-74.

Du, Q., Zhang, S., Song, J., Zhao, Y., & Yang, F. (2020). Activation of porous magnetized

biochar by artificial humic acid for effective removal of lead ions. Journal of Hazardous

Materials, 122115.

Dubé, C. D., & Guiot, S. R. (2015). Direct interspecies electron transfer in anaerobic digestion: a

review. In Biogas Science and Technology (pp. 101-115). Springer, Cham.

Dudek, M., Świechowski, K., Manczarski, P., Koziel, J. A., & Białowiec, A. (2019). The Effect

of Biochar Addition on the Biogas Production Kinetics from the Anaerobic Digestion of

Brewers’ Spent Grain. Energies, 12(8), 1518.

Ebner, J.H., Rankin, M.J., Pronto, J., Labatut, R., Gooch, C., Williamson, A.A. and Trabold, T.A.

(2015). Lifecycle greenhouse gas analysis of an anaerobic codigestion facility processing

dairy manure and industrial food waste. Environmental Science and Technology, Vol. 49,

11199-11208.

Elkhalifa, S., Al-Ansari, T., Mackey, H. R., & McKay, G. (2019). Food waste to biochars

through pyrolysis: A review. Resources, Conservation and Recycling, 144, 310-320.

Enahoro, D. K., & Gloy, B. A. (2008). Economic Analysis of Anaerobic Digestion Systems and

the Financial Incentives provided by the New York State Renewable Portfolio Standard

(RPS) Customer-Sited Tier (CST) Anaerobic Digester Gas (ADG)-to-Electricity

Program.

EREF, Environmental Research & Education Foundation (2019). Analysis of MSW landfill

tipping fees - April 2018.

72

Fagbohungbe, M. O., Herbert, B. M., Hurst, L., Ibeto, C. N., Li, H., Usmani, S. Q., & Semple, K.

T. (2017). The challenges of anaerobic digestion and the role of biochar in optimizing

anaerobic digestion. Waste management, 61, 236-249.

Fagbohungbe, M. O., Herbert, B. M., Hurst, L., Li, H., Usmani, S. Q., & Semple, K. T. (2016).

Impact of biochar on the anaerobic digestion of citrus peel waste. Bioresource

technology, 216, 142-149.

Giwa, A. S., Xu, H., Chang, F., Wu, J., Li, Y., Ali, N., . . . Wang, K. (2019). Effect of biochar on

reactor performance and methane generation during the anaerobic digestion of food waste

treatment at long-run operations. Journal of Environmental Chemical Engineering, 7(4),

103067.

Gupta, S., Kua, H. W., & Koh, H. J. (2018). Application of biochar from food and wood waste as

green admixture for cement mortar. Science of the Total Environment, 619, 419-435.

Hansen, K. H., Angelidaki, I., & Ahring, B. K. (1999). Improving thermophilic anaerobic

digestion of swine manure. Water research, 33(8), 1805-1810.

Indren, M., Birzer, C. H., Kidd, S. P., Hall, T., & Medwell, P. R. (2020). Effects of biochar

parent material and microbial pre-loading in biochar-amended high-solids anaerobic

digestion. Bioresource technology, 298, 122457.

Inthapanya, S., Preston, T., & Leng, R. (2012). Biochar increases biogas production in a batch

digester charged with cattle manure. Livest. Res. Rural Dev, 24(12), 212.

Inyang, M., Gao, B., Pullammanappallil, P., Ding, W., & Zimmerman, A. R. (2010). Biochar

from anaerobically digested sugarcane bagasse. Bioresource technology, 101(22), 8868-

8872.

Jang, H. M., Choi, Y.-K., & Kan, E. (2018). Effects of dairy manure-derived biochar on

psychrophilic, mesophilic and thermophilic anaerobic digestions of dairy manure.


Kumar, S., Jain, M., & Chhonkar, P. (1987). A note on stimulation of biogas production from

cattle dung by addition of charcoal. Biological wastes, 20(3), 209-215.

Li, Q., Xu, M., Wang, G., Chen, R., Qiao, W., & Wang, X. (2018). Biochar assisted thermophilic

co-digestion of food waste and waste activated sludge under high feedstock to seed

sludge ratio in batch experiment. Bioresource technology, 249, 1009-1016.

73

Liang, Y., Qiu, L., Guo, X., Pan, J., Lu, W., & Ge, Y. (2017). Start-up performance of chicken

manure anaerobic digesters amended with biochar and operated at different temperatures.

Nature Environment and Pollution Technology, 16(2), 615.

Linville, J. L., Shen, Y., Ignacio-de Leon, P. A., Schoene, R. P., & Urgun-Demirtas, M. (2017).

In-situ biogas upgrading during anaerobic digestion of food waste amended with walnut

shell biochar at bench scale. Waste Management & Research, 35(6), 669-679.

Lü, F., Liu, Y., Shao, L., & He, P. (2019). Powdered biochar doubled microbial growth in

anaerobic digestion of oil. Applied energy, 247, 605-614.

Lü, F., Luo, C., Shao, L., & He, P. (2016). Biochar alleviates combined stress of ammonium and

acids by firstly enriching Methanosaeta and then Methanosarcina. Water research, 90, 34-

43.

Luo, C., Lü, F., Shao, L., & He, P. (2015). Application of eco-compatible biochar in anaerobic

digestion to relieve acid stress and promote the selective colonization of functional

microbes. Water research, 68, 710-718.

Luz, F. C., Cordiner, S., Manni, A., Mulone, V., & Rocco, V. (2018a). Biochar characteristics

and early applications in anaerobic digestion-a review. Journal of Environmental

Chemical Engineering, 6(2), 2892-2909.

Luz, F. C., Cordiner, S., Manni, A., Mulone, V., Rocco, V., Braglia, R., & Canini, A. (2018b).

Ampelodesmos mauritanicus pyrolysis biochar in anaerobic digestion process: Evaluation

of the biogas yield. Energy, 161, 663-669.

Ma, J., Pan, J., Qiu, L., Wang, Q., & Zhang, Z. (2019). Biochar triggering multipath

methanogenesis and subdued propionic acid accumulation during semi-continuous

anaerobic digestion. Bioresource technology, 293, 122026.

Mainardis, M., Flaibani, S., Mazzolini, F., Peressotti, A., & Goi, D. (2019). Techno-economic

analysis of anaerobic digestion implementation in small Italian breweries and evaluation

of biochar and granular activated carbon addition effect on methane yield. Journal of

Environmental Chemical Engineering, 7(3), 103184.

Masebinu, S., Akinlabi, E., Muzenda, E., & Aboyade, A. (2019). A review of biochar properties

and their roles in mitigating challenges with anaerobic digestion. Renewable and

Sustainable Energy Reviews, 103, 291-307.

74

Meyer-Kohlstock, D., Haupt, T., Heldt, E., Heldt, N., & Kraft, E. (2016). Biochar as additive in

biogas-production from bio-waste. Energies, 9(4), 247.

Mumme, J., Srocke, F., Heeg, K., & Werner, M. (2014). Use of biochars in anaerobic digestion.


Novak, J. M., Lima, I., Xing, B., Gaskin, J. W., Steiner, C., Das, K., . . . Busscher, W. J. (2009).

Characterization of designer biochar produced at different temperatures and their effects

on a loamy sand. Annals of Environmental Science.

Pan, J., Ma, J., Liu, X., Zhai, L., Ouyang, X., & Liu, H. (2019). Effects of different types of

biochar on the anaerobic digestion of chicken manure. Bioresource technology, 275, 258-

265.

Paritosh, K., & Vivekanand, V. (2019). Biochar enabled syntrophic action: Solid state anaerobic

digestion of agricultural stubble for enhanced methane production. Bioresource

technology, 289, 121712.

Park, J. H., Kang, H. J., Park, K. H., & Park, H. D. (2018). Direct interspecies electron transfer via

conductive materials: a perspective for anaerobic digestion applications. Bioresource


Pecchi, M., & Baratieri, M. (2019). Coupling anaerobic digestion with gasification, pyrolysis or

hydrothermal carbonization: A review. Renewable and Sustainable Energy Reviews, 105,

462-475.

Perez Garcia, A. (2014). Techno-economic feasibility study of a small-scale biogas plant for

treating market waste in the city of El Alto.

Qin, Y., Wang, H., Li, X., Cheng, J. J., & Wu, W. (2017). Improving methane yield from organic

fraction of municipal solid waste (OFMSW) with magnetic rice-straw biochar.


Qiu, L., Deng, Y., Wang, F., Davaritouchaee, M., & Yao, Y. (2019). A review on biochar-

mediated anaerobic digestion with enhanced methane recovery. Renewable and

Sustainable Energy Reviews, 115, 109373.

Rafiq, M. K., Bachmann, R. T., Rafiq, M. T., Shang, Z., Joseph, S., & Long, R. (2016). Influence

of pyrolysis temperature on physico-chemical properties of corn stover (Zea mays L.)

biochar and feasibility for carbon capture and energy balance. PloS one, 11(6).

75

Rasapoor, M., Young, B., Asadov, A., Brar, R., Sarmah, A. K., Zhuang, W.-Q., & Baroutian, S.

(2020). Effects of biochar and activated carbon on biogas generation: A

thermogravimetric and chemical analysis approach. Energy Conversion and Management,

203, 112221.

Rodriguez Alberto, D. R., Repa, K. S., Hegde, S., Miller, C. W., & Trabold, T. A. (2019). Novel

Production of Magnetite Particles via Thermochemical Processing of Digestate From

Manure and Food Waste. IEEE Magnetics Letters, 10, 1-5.

Shanmugam, S. R., Adhikari, S., Nam, H., & Sajib, S. K. (2018). Effect of bio-char on methane

generation from glucose and aqueous phase of algae liquefaction using mixed anaerobic

cultures. Biomass and Bioenergy, 108, 479-486.

Shao, L., Li, S., Cai, J., He, P., & Lü, F. (2019). Ability of biochar to facilitate anaerobic

digestion is restricted to stressed surroundings. Journal of Cleaner Production, 238,

117959.

Shen, R., Jing, Y., Feng, J., Luo, J., Yu, J., & Zhao, L. (2020). Performance of enhanced

anaerobic digestion with different pyrolysis biochars and microbial communities.

Bioresource technology, 296, 122354.

Shen, Y., Forrester, S., Koval, J., & Urgun-Demirtas, M. (2017). Yearlong semi-continuous

operation of thermophilic two-stage anaerobic digesters amended with biochar for

enhanced biomethane production. Journal of Cleaner Production, 167, 863-874.

Shen, Y., Linville, J. L., Ignacio-de Leon, P. A. A., Schoene, R. P., & Urgun-Demirtas, M.

(2016). Towards a sustainable paradigm of waste-to-energy process: Enhanced anaerobic

digestion of sludge with woody biochar. Journal of Cleaner Production, 135, 1054-1064.

Shen, Y., Linville, J. L., Urgun-Demirtas, M., Schoene, R. P., & Snyder, S. W. (2015).

Producing pipeline-quality biomethane via anaerobic digestion of sludge amended with

corn stover biochar with in-situ CO2 removal. Applied energy, 158, 300-309.

Sunyoto, N. M., Zhu, M., Zhang, Z., & Zhang, D. (2016). Effect of biochar addition on hydrogen

and methane production in two-phase anaerobic digestion of aqueous carbohydrates food

waste. Bioresource technology, 219, 29-36.

Tomczyk, A., Sokołowska, Z., & Boguta, P. (2020). Biochar physicochemical properties:

pyrolysis temperature and feedstock kind effects. Reviews in Environmental Science and

Bio/Technology, 1-25.

76

Torri, C., & Fabbri, D. (2014). Biochar enables anaerobic digestion of aqueous phase from

intermediate pyrolysis of biomass. Bioresource technology, 172, 335-341.

Towler, G., & Sinnott, R. (2012). Chemical engineering design: principles, practice and

economics of plant and process design. Elsevier.

Trabold, T., & Babbitt, C. W. (2018). Sustainable food waste-to-energy systems: Academic

Press.

USDA, U.S. Department of Agriculture. (2007). An analysis of energy produuction costs from

anaerobic digestion systems on U.S. livestock production facilities.

Viggi, C. C., Simonetti, S., Palma, E., Pagliaccia, P., Braguglia, C., Fazi, S., . . . Koch, C. (2017).

Enhancing methane production from food waste fermentate using biochar: the added

value of electrochemical testing in pre-selecting the most effective type of biochar.

Biotechnology for biofuels, 10(1), 303.

Wang, C., Liu, Y., Gao, X., Chen, H., Xu, X., & Zhu, L. (2018). Role of biochar in the

granulation of anaerobic sludge and improvement of electron transfer characteristics.


Wang, G., Li, Q., Gao, X., & Wang, X. C. (2018). Synergetic promotion of syntrophic methane

production from anaerobic digestion of complex organic wastes by biochar: Performance

and associated mechanisms. Bioresource technology, 250, 812-820.

Wang, G., Li, Q., Li, Y., Xing, Y., Yao, G., Liu, Y., . . . Wang, X. C. (2020). Redox-active

biochar facilitates potential electron tranfer between syntrophic partners to enhance

anaerobic digestion under high organic loading rate. Bioresource technology, 298,

122524.

Watanabe, R., Tada, C., Baba, Y., Fukuda, Y., & Nakai, Y. (2013). Enhancing methane

production during the anaerobic digestion of crude glycerol using Japanese cedar

charcoal. Bioresource technology, 150, 387-392.

Weber, K., & Quicker, P. (2018). Properties of biochar. Fuel, 217, 240-261.

Wei, W., Guo, W., Ngo, H. H., Mannina, G., Wang, D., Chen, X., . . . Ni, B.-J. (2020). Enhanced

high-quality biomethane production from anaerobic digestion of primary sludge by corn

stover biochar. Bioresource technology, 123159.

77

Win, S.S., Hegde, S., Chen, R.B. & Trabold, T.A., “Feasibility assessment of low-volume

anaerobic digestion systems for institutional food waste producers,” Proceedings of the

ASME Power and Energy Conversion Conference, Paper PowerEnergy2017-3126,

Charlotte, NC, June 26 – 30, 2017.

Wu, B., Yang, Q., Yao, F., Chen, S., He, L., Hou, K., . . . Wang, D. (2019a). Evaluating the

effect of biochar on mesophilic anaerobic digestion of waste activated sludge and

microbial diversity. Bioresource technology, 294, 122235.

Wu, B., Yang, Q., Yao, F., Chen, S., He, L., Hou, K., . . . Wang, D. (2019b). Evaluating the

effect of biochar on mesophilic anaerobic digestion of waste activated sludge and

microbial diversity. Bioresource technology, 122235.

Xia, T., Gao, X., Wang, C., Xu, X., & Zhu, L. (2016). An enhanced anaerobic membrane

bioreactor treating bamboo industry wastewater by bamboo charcoal addition:

performance and microbial community analysis. Bioresource technology, 220, 26-33.

Xie, T., Reddy, K. R., Wang, C., Yargicoglu, E., & Spokas, K. (2015). Characteristics and

applications of biochar for environmental remediation: a review. Critical Reviews in

Environmental Science and Technology, 45(9), 939-969.

Yakovlev, V. V., Allan, S. M., Fall, M. L., Shulman, H. S., & Tao, J. (2011). Computational

study of thermal runaway in microwave processing of zirconia. Microwave and RF

Power Applications, 303-306.

Yang, Y., Zhang, Y., Li, Z., Zhao, Z., Quan, X., & Zhao, Z. (2017). Adding granular activated

carbon into anaerobic sludge digestion to promote methane production and sludge

decomposition. Journal of Cleaner Production, 149, 1101-1108.

Ye, M., Liu, J., Ma, C., Li, Y.-Y., Zou, L., Qian, G., & Xu, Z. P. (2018). Improving the stability

and efficiency of anaerobic digestion of food waste using additives: a critical review.

Journal of Cleaner Production, 192, 316-326.

Yin, Z., Xu, S., Liu, S., Xu, S., Li, J., & Zhang, Y. (2020). A novel magnetic biochar prepared by

K2FeO4-promoted oxidative pyrolysis of pomelo peel for adsorption of hexavalent

chromium. Bioresource technology, 300, 122680.

Yun, S., Fang, W., Du, T., Hu, X., Huang, X., Li, X., . . . Lund, P. D. (2018). Use of bio-based

carbon materials for improving biogas yield and digestate stability. Energy, 164, 898-909.

78

Zhang, J., Zhao, W., Zhang, H., Wang, Z., Fan, C., & Zang, L. (2018). Recent achievements in

enhancing anaerobic digestion with carbon-based functional materials. Bioresource


Zhang, L., Li, F., Kuroki, A., Loh, K.-C., Wang, C.-H., Dai, Y., & Tong, Y. W. (2020a).

Methane yield enhancement of mesophilic and thermophilic anaerobic co-digestion of

algal biomass and food waste using algal biochar: Semi-continuous operation and

microbial community analysis. Bioresource technology, 302, 122892.

Zhang, L., Li, F., Kuroki, A., Loh, K.-C., Wang, C.-H., Dai, Y., & Tong, Y. W. (2020b).

Methane yield enhancement of mesophilic and thermophilic anaerobic co-digestion of

algal biomass and food waste using algal biochar: Semi-continuous operation and

microbial community analysis. Bioresource technology, 122892.

Zhang, L., Lim, E. Y., Loh, K.-C., Ok, Y. S., Lee, J. T., Shen, Y., . . . Tong, Y. W. (2020).

Biochar enhanced thermophilic anaerobic digestion of food waste: Focusing on biochar

particle size, microbial community analysis and pilot-scale application. Energy

Conversion and Management, 209, 112654.

Zhao, Z., Zhang, Y., Woodard, T., Nevin, K., & Lovley, D. (2015). Enhancing syntrophic

metabolism in up-flow anaerobic sludge blanket reactors with conductive carbon

materials. Bioresource technology, 191, 140-145.

79

APPENDIX A

RAW BIOMETHANE (BMP) DATA AND EXAMPLE CALCULATION

Appendix A.1: Food waste biochar raw data

Figure A.1 – FWBC biogas production raw data

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30

Bio

gas

(m

l/gV

S)

Days

Inoculum 1 Inoculum 2 Inoculum 2 CelluloseCelullose Cellulose Dog Food 2 Dosg Food 3FWBC500 0.5% 1 FWBC500 0.5% 2 FWBC500 0.5% 3 FWBC500 1% 1FWBC500 1% 2 FWBC500 1% 3 FWBC500 2% 1 FWBC500 2% 2FWBC500 2% 3 FWBC800 0.5% 1 FWBC800 0.5% 2 FWBC800 0.5% 3FWBC800 1% 1 FWBC800 1% 2 FWBC800 1% 3 FWBC800 2% 1

80

Figure A. 2 – Average FWBC biogas production raw data

Figure A. 3 – Average FWBC biogas production from day 11-30

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35

Bio

gas

(N

mL

/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

FWBC500 0.5%

FWBC500 1%

FWBC500 2%

FWBC800 0.5%

FWBC800 1%

FWBC800 2%

0

100

200

300

400

500

600

700

800

10 15 20 25 30

Bio

gas

(N

mL

/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

FWBC500 0.5%

FWBC500 1%

FWBC500 2%

FWBC800 0.5%

FWBC800 1%

FWBC800 2%

81

Table A. 1 – Raw data from FWBC run

82

Appendix A.2: Dry manure biochar raw data

Figure A.4 – DMBC biogas production raw data

0

100

200

300

400

500

600

700

0 5 10 15 20 25 30

Bio

gas

(m

l/gV

S)

Time (days)

innoculum (blank) innoculum (blank) cellulose (control) cellulose (control)cellulose (control) Dog Food 0% Dog Food 0% Dog Food 0%DMBC500 0.5% DMBC500 0.5% DMBC500 0.5% DMBC500 1%DMBC500 1% DMBC500 1% DMBC500 2% DMBC500 2%DMBC500 2% DMBC800 0.5% DMB5800 0.5% DMBC800 0.5%DMBC800 1% DMBC800 1% DMBC800 1% DMBC800 2%

83

Figure A.5 – Average DMBC biogas production raw data

Figure A.6 – Average DMBC biogas production from day 11-30

0

100

200

300

400

500

600

0 5 10 15 20 25 30 35

Bio

gas

(N

mL

/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

DMBC500 0.5%

DMBC500 1%

DMBC500 2%

DMBC800 0.5%

DMBC800 1%

DMBC800 2%

0

100

200

300

400

500

600

10 15 20 25 30

Bio

gas

(N

mL

/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

DMBC500 0.5%

DMBC500 1%

DMBC500 2%

DMBC800 0.5%

DMBC800 1%

DMBC800 2%

84

Table A.2 – Raw data from the DMBC run

85

Appendix A.3: Magnetic biochar raw data

Figure A.7 – MGBC biogas production raw data

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25 30

Bio

gas

(m

l/gV

S)

Time (days)

innoculum (blank) innoculum (blank) cellulose (control) cellulose (control)cellulose (control) Dog Food 0% Dog Food 0% Dog Food 0%MGBC500 0.5% MGBC500 0.5% MGBC500 0.5% MGBC500 1%MGBC500 1% MGBC500 1% MGBC500 2% MGBC500 2%MGBC500 2% MGBC800 0.5% MGB5800 0.5% MGBC800 0.5%

86

Figure A.8 – Average MGBC biogas production raw data

Figure A.9 – Average MGBC biogas production from day 11-30

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25 30

Bio

gas

(Nm

L/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

MGBC500 0.5%

MGBC500 1%

MGBC500 2%

MGBC800 0.5%

MGBC800 1%

MGBC800 2%

0

100

200

300

400

500

600

700

800

900

1000

10 15 20 25 30

Bio

gas

(Nm

L/gV

S)

Time (days)

Inoculum

Cellulose

Dog Food

MGBC500 0.5%

MGBC500 1%

MGBC500 2%

MGBC800 0.5%

MGBC800 1%

MGBC800 2%

87

Table A.3 – Raw data from the MGBC run

88

Appendix A.4: Lag phase analysis

The initial lag phase during anaerobic digestion determines the initial bacterial activation and

provides a head start in the production of biogas. To have a clearer view of these differences, the

first five runs have been highlighted in Figure B.10. Dog food was shown to have a relatively short

lag phase when compared to cellulose (around 3 days). Figure B.10a reports the results obtained

from FWBC, and there is no discernible differences in lag time with biochar addition. Similar

results were found with dry manure and digestate biochar (Figures B.10b and B.10c, respectively).

This suggests that there is a need to perform a more in-depth study including a mathematical kinetic

model based on the Gompertz relation employed by many of the studies cited in Table 1.1.

(a)

0

100

200

300

400

500

600

0 1 2 3 4 5 6

Inoculum Cellulose Dog Food

FWBC500 0.5% FWBC500 1% FWBC500 2%

FWBC800 0.5% FWBC800 1% FWBC800 2%

89

(b)

(c)

Figure A.10 – Lag phase for biogas from runs (a) FWBC, (b) DMBC, (c) MGBC

0

50

100

150

200

250

300

350

400

450

500

0 1 2 3 4 5 6

Bio

gas

(Nm

L/gV

S)

Time (days)Inoculum Cellulose Dog FoodDMBC500 0.5% DMBC500 1% DMBC500 2%DMBC800 0.5% DMBC800 1% DMBC800 2%

0

100

200

300

400

500

600

700

800

0 1 2 3 4 5 6

Bio

gas

(Nm

L/gV

S)

Time (days)

Inoculum Cellulose Dog FoodMGBC500 0.5% MGBC500 1% MGBC500 2%MGBC800 0.5% MGBC800 1% MGBC800 2%

90

Appendix A.5: Example calculation of BMP


𝑔𝑉𝑠] =

𝑉𝑠−𝑉𝑏 ×(𝑚𝐼𝑠𝑚𝐼𝑏

)

𝑚𝑆𝑠,𝑉𝑠

[Equation 3.3]

where

BMP = biomethane potential, the normalized volume of methane produced per gram of volatile

solids (NmL/gVS)

Vs = cumulative volume of methane produced from the reactor with the sample (NmL)

Vb = mean value of cumulative volume of methane produced by the three blanks (NmL)

mIs = total amount of inoculum in the sample (g)

mIb = total amount of inoculum in the blank (g)

mVS,Ss = amount of organic material of substrate contained in the sample bottle (gVS).

Example:

Vs = 465.3 mL CH4

Vb = 160.3 mL CH4

mIs = 301.1 g

mIb = 289.4 g

mVS,Ss = 0.97 gVS


𝑔𝑉𝑠] =

465.3 𝑚𝐿 𝐶𝐻4 − 160.3 𝑚𝐿 𝐶𝐻4 × (301.1 𝑔289.4 𝑔)

0.97 𝑔𝑉𝑆

= 327.15𝑚𝐿 𝐶𝐻4

𝑔𝑉𝑆

91

APPENDIX B

NET PRESENT VALUE EXAMPLE CALCULATION

𝑁𝑃𝑉 = −𝐼 + ∑𝐶𝐹𝑡

(1+𝑖)𝑡𝑇𝑡=1

where:

I = initial capital investment (for biochar metering equipment, and also pyrolysis system

for Scenario 1)

CFt = cash flow (revenue – cost) for each year t

I = discount rate = 2.5% (Table 4.3)

t = year

Scenario 3a. BUY mid biochar price ($200/ton of biochar) + 20% more FW income

Income $/year Calculated NPV

Electricity Sold $ 22,869.11 $ 9,935,554.71

Saved Heat income $ 8,120.41

Tipping fees $ 614,334.08

Carbon Credit $ 4,805.20

Variable REC $ 146,131.65 Total income $ 796,260.44

Costs $/year

Cost of buying Biochar $ (154,715.78) Total cost $ (155,715.78)

cost of mixer $ (50,000.00)

O&M py $ (1,000.00) Annual cash flow $ 640,544.66

*Values in parenthesis are negative since they are costs

Discount rate (i) .025

Discount factor (1+i) 1.025

NPV denominator for 20 yrs (1+i)^20 15.58916229

Annual Cash Flow = Total income + Total cost = $796,260.44 - $155,715.78 = $640,544.66

NPV = - Cost of buying biochar + annual cash flow(1+i)^20

NPV = -$154,175.78 + ($640,544.66*15.58916229) = $ 9,935,554.71

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